diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index d50e440c5e935..b94af15f7e19c 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -5,6 +5,12 @@ module ts {
     let nextNodeId = 1;
     let nextMergeId = 1;
 
+    // @internal
+    export function getNodeId(node: Node): number {
+        if (!node.id) node.id = nextNodeId++;
+        return node.id;
+    }
+
     /* @internal */ export let checkTime = 0;
 
     export function createTypeChecker(host: TypeCheckerHost, produceDiagnostics: boolean): TypeChecker {
@@ -255,8 +261,8 @@ module ts {
         }
 
         function getNodeLinks(node: Node): NodeLinks {
-            if (!node.id) node.id = nextNodeId++;
-            return nodeLinks[node.id] || (nodeLinks[node.id] = {});
+            let nodeId = getNodeId(node);
+            return nodeLinks[nodeId] || (nodeLinks[nodeId] = {});
         }
 
         function getSourceFile(node: Node): SourceFile {
@@ -10954,134 +10960,7 @@ module ts {
             return symbol.flags & SymbolFlags.ValueModule && symbol.declarations.length === 1 && symbol.declarations[0].kind === SyntaxKind.SourceFile;
         }
 
-        function isNodeDescendentOf(node: Node, ancestor: Node): boolean {
-            while (node) {
-                if (node === ancestor) return true;
-                node = node.parent;
-            }
-            return false;
-        }
-
-        function isUniqueLocalName(name: string, container: Node): boolean {
-            for (let node = container; isNodeDescendentOf(node, container); node = node.nextContainer) {
-                if (node.locals && hasProperty(node.locals, name)) {
-                    // We conservatively include alias symbols to cover cases where they're emitted as locals
-                    if (node.locals[name].flags & (SymbolFlags.Value | SymbolFlags.ExportValue | SymbolFlags.Alias)) {
-                        return false;
-                    }
-                }
-            }
-            return true;
-        }
-
-        function getGeneratedNamesForSourceFile(sourceFile: SourceFile): Map<string> {
-            let links = getNodeLinks(sourceFile);
-            let generatedNames = links.generatedNames;
-            if (!generatedNames) {
-                generatedNames = links.generatedNames = {};
-                generateNames(sourceFile);
-            }
-            return generatedNames;
-
-            function generateNames(node: Node) {
-                switch (node.kind) {
-                    case SyntaxKind.FunctionDeclaration:
-                    case SyntaxKind.ClassDeclaration:
-                        generateNameForFunctionOrClassDeclaration(<Declaration>node);
-                        break;
-                    case SyntaxKind.ModuleDeclaration:
-                        generateNameForModuleOrEnum(<ModuleDeclaration>node);
-                        generateNames((<ModuleDeclaration>node).body);
-                        break;
-                    case SyntaxKind.EnumDeclaration:
-                        generateNameForModuleOrEnum(<EnumDeclaration>node);
-                        break;
-                    case SyntaxKind.ImportDeclaration:
-                        generateNameForImportDeclaration(<ImportDeclaration>node);
-                        break;
-                    case SyntaxKind.ExportDeclaration:
-                        generateNameForExportDeclaration(<ExportDeclaration>node);
-                        break;
-                    case SyntaxKind.ExportAssignment:
-                        generateNameForExportAssignment(<ExportAssignment>node);
-                        break;
-                    case SyntaxKind.SourceFile:
-                    case SyntaxKind.ModuleBlock:
-                        forEach((<SourceFile | ModuleBlock>node).statements, generateNames);
-                        break;
-                }
-            }
-
-            function isExistingName(name: string) {
-                return hasProperty(globals, name) ||  hasProperty(sourceFile.identifiers, name) || hasProperty(generatedNames, name);
-            }
-
-            function makeUniqueName(baseName: string): string {
-                let name = generateUniqueName(baseName, isExistingName);
-                return generatedNames[name] = name;
-            }
-
-            function assignGeneratedName(node: Node, name: string) {
-                getNodeLinks(node).generatedName = unescapeIdentifier(name);
-            }
-
-            function generateNameForFunctionOrClassDeclaration(node: Declaration) {
-                if (!node.name) {
-                    assignGeneratedName(node, makeUniqueName("default"));
-                }
-            }
-
-            function generateNameForModuleOrEnum(node: ModuleDeclaration | EnumDeclaration) {
-                if (node.name.kind === SyntaxKind.Identifier) {
-                    let name = node.name.text;
-                    // Use module/enum name itself if it is unique, otherwise make a unique variation
-                    assignGeneratedName(node, isUniqueLocalName(name, node) ? name : makeUniqueName(name));
-                }
-            }
-
-            function generateNameForImportOrExportDeclaration(node: ImportDeclaration | ExportDeclaration) {
-                let expr = getExternalModuleName(node);
-                let baseName = expr.kind === SyntaxKind.StringLiteral ?
-                    escapeIdentifier(makeIdentifierFromModuleName((<LiteralExpression>expr).text)) : "module";
-                assignGeneratedName(node, makeUniqueName(baseName));
-            }
-
-            function generateNameForImportDeclaration(node: ImportDeclaration) {
-                if (node.importClause && node.importClause.namedBindings && node.importClause.namedBindings.kind === SyntaxKind.NamedImports) {
-                    generateNameForImportOrExportDeclaration(node);
-                }
-            }
-
-            function generateNameForExportDeclaration(node: ExportDeclaration) {
-                if (node.moduleSpecifier) {
-                    generateNameForImportOrExportDeclaration(node);
-                }
-            }
-
-            function generateNameForExportAssignment(node: ExportAssignment) {
-                if (node.expression && node.expression.kind !== SyntaxKind.Identifier) {
-                    assignGeneratedName(node, makeUniqueName("default"));
-                }
-            }
-        }
-
-        function getGeneratedNameForNode(node: Node) {
-            let links = getNodeLinks(node);
-            if (!links.generatedName) {
-                getGeneratedNamesForSourceFile(getSourceFile(node));
-            }
-            return links.generatedName;
-        }
-
-        function getLocalNameOfContainer(container: ModuleDeclaration | EnumDeclaration): string {
-            return getGeneratedNameForNode(container);
-        }
-
-        function getLocalNameForImportDeclaration(node: ImportDeclaration): string {
-            return getGeneratedNameForNode(node);
-        }
-
-        function getAliasNameSubstitution(symbol: Symbol): string {
+        function getAliasNameSubstitution(symbol: Symbol, getGeneratedNameForNode: (Node: Node) => string): string {
             let declaration = getDeclarationOfAliasSymbol(symbol);
             if (declaration && declaration.kind === SyntaxKind.ImportSpecifier) {
                 let moduleName = getGeneratedNameForNode(<ImportDeclaration>declaration.parent.parent.parent);
@@ -11090,7 +10969,7 @@ module ts {
             }
         }
 
-        function getExportNameSubstitution(symbol: Symbol, location: Node): string {
+        function getExportNameSubstitution(symbol: Symbol, location: Node, getGeneratedNameForNode: (Node: Node) => string): string {
             if (isExternalModuleSymbol(symbol.parent)) {
                 var symbolName = unescapeIdentifier(symbol.name);
                 // If this is es6 or higher, just use the name of the export
@@ -11112,24 +10991,24 @@ module ts {
             }
         }
 
-        function getExpressionNameSubstitution(node: Identifier): string {
+        function getExpressionNameSubstitution(node: Identifier, getGeneratedNameForNode: (Node: Node) => string): string {
             let symbol = getNodeLinks(node).resolvedSymbol;
             if (symbol) {
                 // Whan an identifier resolves to a parented symbol, it references an exported entity from
                 // another declaration of the same internal module.
                 if (symbol.parent) {
-                    return getExportNameSubstitution(symbol, node.parent);
+                    return getExportNameSubstitution(symbol, node.parent, getGeneratedNameForNode);
                 }
                 // If we reference an exported entity within the same module declaration, then whether
                 // we prefix depends on the kind of entity. SymbolFlags.ExportHasLocal encompasses all the
                 // kinds that we do NOT prefix.
                 let exportSymbol = getExportSymbolOfValueSymbolIfExported(symbol);
                 if (symbol !== exportSymbol && !(exportSymbol.flags & SymbolFlags.ExportHasLocal)) {
-                    return getExportNameSubstitution(exportSymbol, node.parent);
+                    return getExportNameSubstitution(exportSymbol, node.parent, getGeneratedNameForNode);
                 }
                 // Named imports from ES6 import declarations are rewritten
                 if (symbol.flags & SymbolFlags.Alias && languageVersion < ScriptTarget.ES6) {
-                    return getAliasNameSubstitution(symbol);
+                    return getAliasNameSubstitution(symbol, getGeneratedNameForNode);
                 }
             }
         }
@@ -11232,10 +11111,13 @@ module ts {
             getSymbolDisplayBuilder().buildTypeDisplay(type, writer, enclosingDeclaration, flags);
         }
 
-        function isUnknownIdentifier(location: Node, name: string): boolean {
-            Debug.assert(!nodeIsSynthesized(location), "isUnknownIdentifier called with a synthesized location");
-            return !resolveName(location, name, SymbolFlags.Value, /*nodeNotFoundMessage*/ undefined, /*nameArg*/ undefined) &&
-                !hasProperty(getGeneratedNamesForSourceFile(getSourceFile(location)), name);
+        function hasGlobalName(name: string): boolean {
+            return hasProperty(globals, name);
+        }
+
+        function resolvesToSomeValue(location: Node, name: string): boolean {
+            Debug.assert(!nodeIsSynthesized(location), "resolvesToSomeValue called with a synthesized location");
+            return !!resolveName(location, name, SymbolFlags.Value, /*nodeNotFoundMessage*/ undefined, /*nameArg*/ undefined);
         }
 
         function getBlockScopedVariableId(n: Identifier): number {
@@ -11265,8 +11147,8 @@ module ts {
 
         function createResolver(): EmitResolver {
             return {
-                getGeneratedNameForNode,
                 getExpressionNameSubstitution,
+                hasGlobalName,
                 hasExportDefaultValue,
                 isReferencedAliasDeclaration,
                 getNodeCheckFlags,
@@ -11279,7 +11161,7 @@ module ts {
                 isSymbolAccessible,
                 isEntityNameVisible,
                 getConstantValue,
-                isUnknownIdentifier,
+                resolvesToSomeValue,
                 collectLinkedAliases,
                 getBlockScopedVariableId,
             };
diff --git a/src/compiler/emitter.ts b/src/compiler/emitter.ts
index b62ab7045535b..ad6c6d1c8b649 100644
--- a/src/compiler/emitter.ts
+++ b/src/compiler/emitter.ts
@@ -19,6 +19,14 @@ module ts {
         return isExternalModule(sourceFile) || isDeclarationFile(sourceFile);
     }
 
+    // flag enum used to request and track usages of few dedicated temp variables
+    // enum values are used to set/check bit values and thus should not have bit collisions.
+    const enum TempVariableKind {
+        auto = 0,
+        _i = 1,
+        _n = 2,
+    }
+
     // @internal
     // targetSourceFile is when users only want one file in entire project to be emitted. This is used in compileOnSave feature
     export function emitFiles(resolver: EmitResolver, host: EmitHost, targetSourceFile: SourceFile): EmitResult {
@@ -60,6 +68,26 @@ module ts {
             sourceMaps: sourceMapDataList
         };
 
+        function isNodeDescendentOf(node: Node, ancestor: Node): boolean {
+            while (node) {
+                if (node === ancestor) return true;
+                node = node.parent;
+            }
+            return false;
+        }
+
+        function isUniqueLocalName(name: string, container: Node): boolean {
+            for (let node = container; isNodeDescendentOf(node, container); node = node.nextContainer) {
+                if (node.locals && hasProperty(node.locals, name)) {
+                    // We conservatively include alias symbols to cover cases where they're emitted as locals
+                    if (node.locals[name].flags & (SymbolFlags.Value | SymbolFlags.ExportValue | SymbolFlags.Alias)) {
+                        return false;
+                    }
+                }
+            }
+            return true;
+        }
+
         function emitJavaScript(jsFilePath: string, root?: SourceFile) {
             let writer = createTextWriter(newLine);
             let write = writer.write;
@@ -71,15 +99,17 @@ module ts {
 
             let currentSourceFile: SourceFile;
 
-            let lastFrame: ScopeFrame;
-            let currentScopeNames: Map<string>;
-
-            let generatedBlockScopeNames: string[];
+            let generatedNameSet: Map<string>;
+            let nodeToGeneratedName: string[];
+            let blockScopedVariableToGeneratedName: string[];
 
             let extendsEmitted = false;
+
             let tempCount = 0;
             let tempVariables: Identifier[];
             let tempParameters: Identifier[];
+            let predefinedTempsInUse = TempVariableKind.auto;
+
             let externalImports: ExternalImportInfo[];
             let exportSpecifiers: Map<ExportSpecifier[]>;
             let exportDefault: FunctionDeclaration | ClassDeclaration | ExportAssignment | ExportSpecifier;
@@ -144,81 +174,197 @@ module ts {
                 emit(sourceFile);
             }
 
-            // enters the new lexical environment
-            // return value should be passed to matching call to exitNameScope.
-            function enterNameScope(): boolean {
-                let names = currentScopeNames;
-                currentScopeNames = undefined;
-                if (names) {
-                    lastFrame = { names, previous: lastFrame };
-                    return true;
+            function generateNameForNode(node: Node) {
+                switch (node.kind) {
+                    case SyntaxKind.FunctionDeclaration:
+                    case SyntaxKind.ClassDeclaration:
+                        generateNameForFunctionOrClassDeclaration(<Declaration>node);
+                        break;
+                    case SyntaxKind.ModuleDeclaration:
+                        generateNameForModuleOrEnum(<ModuleDeclaration>node);
+                        generateNameForNode((<ModuleDeclaration>node).body);
+                        break;
+                    case SyntaxKind.EnumDeclaration:
+                        generateNameForModuleOrEnum(<EnumDeclaration>node);
+                        break;
+                    case SyntaxKind.ImportDeclaration:
+                        generateNameForImportDeclaration(<ImportDeclaration>node);
+                        break;
+                    case SyntaxKind.ExportDeclaration:
+                        generateNameForExportDeclaration(<ExportDeclaration>node);
+                        break;
+                    case SyntaxKind.ExportAssignment:
+                        generateNameForExportAssignment(<ExportAssignment>node);
+                        break;
+                    case SyntaxKind.SourceFile:
+                    case SyntaxKind.ModuleBlock:
+                        forEach((<SourceFile | ModuleBlock>node).statements, generateNameForNode);
+                        break;
                 }
-                return false;
             }
 
-            function exitNameScope(popFrame: boolean): void {
-                if (popFrame) {
-                    currentScopeNames = lastFrame.names;
-                    lastFrame = lastFrame.previous;
+            function isUniqueName(name: string): boolean {
+                return !resolver.hasGlobalName(name) &&
+                    !hasProperty(currentSourceFile.identifiers, name) &&
+                    (!generatedNameSet || !hasProperty(generatedNameSet, name))
+            }
+
+            // in cases like
+            // for (var x of []) {
+            //     _i;
+            // }
+            // we should be able to detect if let _i was shadowed by some temp variable that was allocated in scope
+            function nameConflictsWithSomeTempVariable(name: string): boolean {
+                // temp variable names always start with '_'
+                if (name.length < 2 || name.charCodeAt(0) !== CharacterCodes._) {
+                    return false;
+                }
+
+                if (name === "_i") {
+                    return !!(predefinedTempsInUse & TempVariableKind._i);
+                }
+
+                if (name === "_n") {
+                    return !!(predefinedTempsInUse & TempVariableKind._n);
+                }
+
+                if (name.length === 2 && name.charCodeAt(1) >= CharacterCodes.a && name.charCodeAt(1) <= CharacterCodes.z) {
+                    // handles _a .. _z
+                    let n = name.charCodeAt(1) - CharacterCodes.a;
+                    return n < tempCount;
                 }
                 else {
-                    currentScopeNames = undefined;
+                    // handles _1, _2...
+                    let n = +name.substring(1);
+                    return !isNaN(n) && n >= 0 && n < (tempCount - 26);
                 }
             }
 
-            function generateUniqueNameForLocation(location: Node, baseName: string): string {
-                let name: string
-                // first try to check if base name can be used as is
-                if (!isExistingName(location, baseName)) {
-                    name = baseName;
+            // This function generates a name using the following pattern:
+            // _a .. _h, _j ... _z, _0, _1, ...
+            // It is guaranteed that generated name will not shadow any existing user-defined names,
+            // however it can hide another name generated by this function higher in the scope.
+            // NOTE: names generated by 'makeTempVariableName' and 'makeUniqueName' will never conflict.
+            // see comment for 'makeTempVariableName' for more information.
+            function makeTempVariableName(location: Node, tempVariableKind: TempVariableKind): string {
+                let tempName: string;
+                if (tempVariableKind !== TempVariableKind.auto && !(predefinedTempsInUse & tempVariableKind)) {
+                    tempName = tempVariableKind === TempVariableKind._i ? "_i" : "_n";
+                    if (!resolver.resolvesToSomeValue(location, tempName)) {
+                        predefinedTempsInUse |= tempVariableKind;
+                        return tempName;
+                    }
                 }
-                else {
-                    name = generateUniqueName(baseName, n => isExistingName(location, n));
+
+                do {
+                    // Note: we avoid generating _i and _n as those are common names we want in other places.
+                    var char = CharacterCodes.a + tempCount;
+                    if (char !== CharacterCodes.i && char !== CharacterCodes.n) {
+                        if (tempCount < 26) {
+                            tempName = "_" + String.fromCharCode(char);
+                        }
+                        else {
+                            tempName = "_" + (tempCount - 26);
+                        }
+                    }
+
+                    tempCount++;
                 }
-                
-                return recordNameInCurrentScope(name);
+                while (resolver.resolvesToSomeValue(location, tempName));
+
+                return tempName;
             }
-            
-            function recordNameInCurrentScope(name: string): string {
-                if (!currentScopeNames) {
-                    currentScopeNames = {};
+
+            // Generates a name that is unique within current file and does not collide with
+            // any names in global scope.
+            // NOTE: names generated by 'makeTempVariableName' and 'makeUniqueName' will never conflict
+            // because of the way how these names are generated
+            // - makeUniqueName builds a name by picking a base name (which should not be empty string)
+            //   and appending suffix '_<number>'
+            // - makeTempVariableName creates a name using the following pattern:
+            //   _a .. _h, _j ... _z, _0, _1, ...
+            // This means that names from 'makeTempVariableName' will have only one underscore at the beginning
+            // and names from 'makeUniqieName' will have at least one underscore in the middle 
+            // so they will never collide.
+            function makeUniqueName(baseName: string): string {
+                Debug.assert(!!baseName);
+
+                // Find the first unique 'name_n', where n is a positive number
+                if (baseName.charCodeAt(baseName.length - 1) !== CharacterCodes._) {
+                    baseName += "_";
+                }
+
+                let i = 1;
+                let generatedName: string;
+                while (true) {
+                    generatedName = baseName + i;
+                    if (isUniqueName(generatedName)) {
+                        break;
+                    }
+                    i++;
                 }
 
-                return currentScopeNames[name] = name;
+                if (!generatedNameSet) {
+                    generatedNameSet = {};
+                }
+                return generatedNameSet[generatedName] = generatedName;
             }
 
-            function isExistingName(location: Node, name: string) {
-                // check if resolver is aware of this name (if name was seen during the typecheck)
-                if (!resolver.isUnknownIdentifier(location, name)) {
-                    return true;
+            function renameNode(node: Node, name: string): string {
+                var nodeId = getNodeId(node);
+
+                if (!nodeToGeneratedName) {
+                    nodeToGeneratedName = [];
                 }
 
-                // check if name is present in generated names that were introduced by the emitter
-                if (currentScopeNames && hasProperty(currentScopeNames, name)) {
-                    return true;
+                return nodeToGeneratedName[nodeId] = unescapeIdentifier(name);
+            }
+
+            function generateNameForFunctionOrClassDeclaration(node: Declaration) {
+                if (!node.name) {
+                    renameNode(node, makeUniqueName("default"));
                 }
+            }
 
-                // check generated names in outer scopes
-                // let x;
-                // function foo() {
-                //    let x; // 1
-                //    function bar() {
-                //        {
-                //            let x; // 2
-                //        }
-                //        console.log(x); // 3
-                //    }
-                //}
-                // here both x(1) and x(2) should be renamed and their names should be different
-                // so x in (3) will refer to x(1)
-                let frame = lastFrame;
-                while (frame) {
-                    if (hasProperty(frame.names, name)) {
-                        return true;
-                    }
-                    frame = frame.previous;
+            function generateNameForModuleOrEnum(node: ModuleDeclaration | EnumDeclaration) {
+                if (node.name.kind === SyntaxKind.Identifier) {
+                    let name = node.name.text;
+                    // Use module/enum name itself if it is unique, otherwise make a unique variation
+                    renameNode(node, isUniqueLocalName(name, node) ? name : makeUniqueName(name));
+                }
+            }
+
+            function generateNameForImportOrExportDeclaration(node: ImportDeclaration | ExportDeclaration) {
+                let expr = getExternalModuleName(node);
+                let baseName = expr.kind === SyntaxKind.StringLiteral ?
+                    escapeIdentifier(makeIdentifierFromModuleName((<LiteralExpression>expr).text)) : "module";
+                renameNode(node, makeUniqueName(baseName));
+            }
+
+            function generateNameForImportDeclaration(node: ImportDeclaration) {
+                if (node.importClause && node.importClause.namedBindings && node.importClause.namedBindings.kind === SyntaxKind.NamedImports) {
+                    generateNameForImportOrExportDeclaration(node);
+                }
+            }
+
+            function generateNameForExportDeclaration(node: ExportDeclaration) {
+                if (node.moduleSpecifier) {
+                    generateNameForImportOrExportDeclaration(node);
+                }
+            }
+
+            function generateNameForExportAssignment(node: ExportAssignment) {
+                if (node.expression && node.expression.kind !== SyntaxKind.Identifier) {
+                    renameNode(node, makeUniqueName("default"));
                 }
-                return false;
+            }
+
+            function getGeneratedNameForNode(node: Node) {
+                let nodeId = getNodeId(node);
+                if (!nodeToGeneratedName || !nodeToGeneratedName[nodeId]) {
+                    generateNameForNode(node);
+                }
+                return nodeToGeneratedName ? nodeToGeneratedName[nodeId] : undefined;
             }
 
             function initializeEmitterWithSourceMaps() {
@@ -585,32 +731,10 @@ module ts {
                 writeFile(host, diagnostics, jsFilePath, emitOutput, writeByteOrderMark);
             }
 
-            // Create a temporary variable with a unique unused name. The forLoopVariable parameter signals that the
-            // name should be one that is appropriate for a for loop variable.
-            function createTempVariable(location: Node, preferredName?: string): Identifier {
-                for (var name = preferredName; !name || isExistingName(location, name); tempCount++) {
-                    // _a .. _h, _j ... _z, _0, _1, ...
-
-                    // Note: we avoid generating _i and _n as those are common names we want in other places.
-                    var char = CharacterCodes.a + tempCount;
-                    if (char === CharacterCodes.i || char === CharacterCodes.n) {
-                        continue;
-                    }
-
-                    if (tempCount < 26) {
-                        name = "_" + String.fromCharCode(char);
-                    }
-                    else {
-                        name = "_" + (tempCount - 26);
-                    }
-                }
-                
-                // This is necessary so that a name generated via renameNonTopLevelLetAndConst will see the name
-                // we just generated.
-                recordNameInCurrentScope(name);
-                
+            // Create a temporary variable with a unique unused name.
+            function createTempVariable(location: Node, tempVariableKind = TempVariableKind.auto): Identifier {
                 let result = <Identifier>createSynthesizedNode(SyntaxKind.Identifier);
-                result.text = name;
+                result.text = makeTempVariableName(location, tempVariableKind);
                 return result;
             }
 
@@ -621,8 +745,8 @@ module ts {
                 tempVariables.push(name);
             }
 
-            function createAndRecordTempVariable(location: Node, preferredName?: string): Identifier {
-                let temp = createTempVariable(location, preferredName);
+            function createAndRecordTempVariable(location: Node, tempVariableKind?: TempVariableKind): Identifier {
+                let temp = createTempVariable(location, tempVariableKind);
                 recordTempDeclaration(temp);
 
                 return temp;
@@ -1085,7 +1209,7 @@ module ts {
             }
 
             function emitExpressionIdentifier(node: Identifier) {
-                let substitution = resolver.getExpressionNameSubstitution(node);
+                let substitution = resolver.getExpressionNameSubstitution(node, getGeneratedNameForNode);
                 if (substitution) {
                     write(substitution);
                 }
@@ -1095,7 +1219,7 @@ module ts {
             }
 
             function getGeneratedNameForIdentifier(node: Identifier): string {
-                if (nodeIsSynthesized(node) || !generatedBlockScopeNames) {
+                if (nodeIsSynthesized(node) || !blockScopedVariableToGeneratedName) {
                     return undefined;
                 }
 
@@ -1104,7 +1228,7 @@ module ts {
                     return undefined;
                 }
 
-                return generatedBlockScopeNames[variableId];
+                return blockScopedVariableToGeneratedName[variableId];
             }
 
             function emitIdentifier(node: Identifier, allowGeneratedIdentifiers: boolean) {
@@ -1332,7 +1456,7 @@ module ts {
                         // manage by just emitting strings (which is a lot more performant).
                         //let prefix = createIdentifier(resolver.getExpressionNamePrefix((<ShorthandPropertyAssignment>property).name));
                         //return createPropertyAccessExpression(prefix, (<ShorthandPropertyAssignment>property).name);
-                        return createIdentifier(resolver.getExpressionNameSubstitution((<ShorthandPropertyAssignment>property).name));
+                        return createIdentifier(resolver.getExpressionNameSubstitution((<ShorthandPropertyAssignment>property).name, getGeneratedNameForNode));
 
                     case SyntaxKind.MethodDeclaration:
                         return createFunctionExpression((<MethodDeclaration>property).parameters, (<MethodDeclaration>property).body);
@@ -1546,7 +1670,7 @@ module ts {
                         emitExpressionIdentifier(node.name);
                     }
                 }
-                else if (resolver.getExpressionNameSubstitution(node.name)) {
+                else if (resolver.getExpressionNameSubstitution(node.name, getGeneratedNameForNode)) {
                     // Emit identifier as an identifier
                     write(": ");
                     // Even though this is stored as identifier treat it as an expression
@@ -2079,10 +2203,10 @@ module ts {
                 //
                 // we don't want to emit a temporary variable for the RHS, just use it directly.
                 let rhsIsIdentifier = node.expression.kind === SyntaxKind.Identifier;
-                let counter = createTempVariable(node, /*preferredName*/ "_i");
+                let counter = createTempVariable(node, TempVariableKind._i);
                 let rhsReference = rhsIsIdentifier ? <Identifier>node.expression : createTempVariable(node);
 
-                var cachedLength = compilerOptions.cacheDownlevelForOfLength ? createTempVariable(node, /*preferredName:*/ "_n") : undefined;
+                var cachedLength = compilerOptions.cacheDownlevelForOfLength ? createTempVariable(node, TempVariableKind._n) : undefined;
 
                 // This is the let keyword for the counter and rhsReference. The let keyword for
                 // the LHS will be emitted inside the body.
@@ -2323,7 +2447,7 @@ module ts {
 
             function emitContainingModuleName(node: Node) {
                 let container = getContainingModule(node);
-                write(container ? resolver.getGeneratedNameForNode(container) : "exports");
+                write(container ? getGeneratedNameForNode(container) : "exports");
             }
 
             function emitModuleMemberName(node: Declaration) {
@@ -2331,7 +2455,7 @@ module ts {
                 if (getCombinedNodeFlags(node) & NodeFlags.Export) {
                     var container = getContainingModule(node);
                     if (container) {
-                        write(resolver.getGeneratedNameForNode(container));
+                        write(getGeneratedNameForNode(container));
                         write(".");
                     }
                     else if (languageVersion < ScriptTarget.ES6) {
@@ -2673,9 +2797,14 @@ module ts {
 
                 // here it is known that node is a block scoped variable
                 let list = getAncestor(node, SyntaxKind.VariableDeclarationList);
-                if (list.parent.kind === SyntaxKind.VariableStatement && list.parent.parent.kind === SyntaxKind.SourceFile) {
-                    // do not rename variables that are defined on source file level
-                    return;
+                if (list.parent.kind === SyntaxKind.VariableStatement) {
+                    let isSourceFileLevelBinding = list.parent.parent.kind === SyntaxKind.SourceFile;
+                    let isModuleLevelBinding = list.parent.parent.kind === SyntaxKind.ModuleBlock;
+                    let isFunctionLevelBinding =
+                        list.parent.parent.kind === SyntaxKind.Block && isFunctionLike(list.parent.parent.parent);
+                    if (isSourceFileLevelBinding || isModuleLevelBinding || isFunctionLevelBinding) {
+                        return;
+                    }
                 }
 
                 let blockScopeContainer = getEnclosingBlockScopeContainer(node);
@@ -2683,12 +2812,19 @@ module ts {
                     ? blockScopeContainer
                     : blockScopeContainer.parent;
 
-                let generatedName = generateUniqueNameForLocation(parent, (<Identifier>node).text);
-                let variableId = resolver.getBlockScopedVariableId(<Identifier>node);
-                if (!generatedBlockScopeNames) {
-                    generatedBlockScopeNames = [];
+                var hasConflictsInEnclosingScope =
+                    resolver.resolvesToSomeValue(parent, (<Identifier>node).text) ||
+                    nameConflictsWithSomeTempVariable((<Identifier>node).text);
+
+                if (hasConflictsInEnclosingScope) {
+                    let variableId = resolver.getBlockScopedVariableId(<Identifier>node);
+                    if (!blockScopedVariableToGeneratedName) {
+                        blockScopedVariableToGeneratedName = [];
+                    }
+
+                    let generatedName = makeUniqueName((<Identifier>node).text);
+                    blockScopedVariableToGeneratedName[variableId] = generatedName;
                 }
-                generatedBlockScopeNames[variableId] = generatedName;
             }
 
             function isES6ModuleMemberDeclaration(node: Node) {
@@ -2770,7 +2906,7 @@ module ts {
                 if (languageVersion < ScriptTarget.ES6 && hasRestParameters(node)) {
                     let restIndex = node.parameters.length - 1;
                     let restParam = node.parameters[restIndex];
-                    let tempName = createTempVariable(node, /*preferredName:*/ "_i").text;
+                    let tempName = createTempVariable(node, TempVariableKind._i).text;
                     writeLine();
                     emitLeadingComments(restParam);
                     emitStart(restParam);
@@ -2820,7 +2956,7 @@ module ts {
                     emitNodeWithoutSourceMap(node.name);
                 }
                 else {
-                    write(resolver.getGeneratedNameForNode(node));
+                    write(getGeneratedNameForNode(node));
                 }
             }
 
@@ -2906,11 +3042,12 @@ module ts {
                 let saveTempCount = tempCount;
                 let saveTempVariables = tempVariables;
                 let saveTempParameters = tempParameters;
+                let savePredefinedTempsInUse = predefinedTempsInUse;
+
                 tempCount = 0;
                 tempVariables = undefined;
                 tempParameters = undefined;
-
-                let popFrame = enterNameScope()
+                predefinedTempsInUse = TempVariableKind.auto;
 
                 // When targeting ES6, emit arrow function natively in ES6
                 if (shouldEmitAsArrowFunction(node)) {
@@ -2943,8 +3080,7 @@ module ts {
                     write(";");
                 }
 
-                exitNameScope(popFrame);
-
+                predefinedTempsInUse = savePredefinedTempsInUse;
                 tempCount = saveTempCount;
                 tempVariables = saveTempVariables;
                 tempParameters = saveTempParameters;
@@ -3241,11 +3377,12 @@ module ts {
                 let saveTempCount = tempCount;
                 let saveTempVariables = tempVariables;
                 let saveTempParameters = tempParameters;
+                let savePredefinedTempsInUse = predefinedTempsInUse;
                 tempCount = 0;
                 tempVariables = undefined;
                 tempParameters = undefined;
+                predefinedTempsInUse = TempVariableKind.auto;
 
-                let popFrame = enterNameScope();
                 // Check if we have property assignment inside class declaration.
                 // If there is property assignment, we need to emit constructor whether users define it or not
                 // If there is no property assignment, we can omit constructor if users do not define it
@@ -3354,8 +3491,7 @@ module ts {
                     emitTrailingComments(ctor);
                 }
 
-                exitNameScope(popFrame);
-
+                predefinedTempsInUse = savePredefinedTempsInUse;
                 tempCount = saveTempCount;
                 tempVariables = saveTempVariables;
                 tempParameters = saveTempParameters;
@@ -3494,7 +3630,7 @@ module ts {
                 emitStart(node);
                 write("(function (");
                 emitStart(node.name);
-                write(resolver.getGeneratedNameForNode(node));
+                write(getGeneratedNameForNode(node));
                 emitEnd(node.name);
                 write(") {");
                 increaseIndent();
@@ -3531,9 +3667,9 @@ module ts {
             function emitEnumMember(node: EnumMember) {
                 let enumParent = <EnumDeclaration>node.parent;
                 emitStart(node);
-                write(resolver.getGeneratedNameForNode(enumParent));
+                write(getGeneratedNameForNode(enumParent));
                 write("[");
-                write(resolver.getGeneratedNameForNode(enumParent));
+                write(getGeneratedNameForNode(enumParent));
                 write("[");
                 emitExpressionForPropertyName(node.name);
                 write("] = ");
@@ -3586,19 +3722,20 @@ module ts {
                 emitStart(node);
                 write("(function (");
                 emitStart(node.name);
-                write(resolver.getGeneratedNameForNode(node));
+                write(getGeneratedNameForNode(node));
                 emitEnd(node.name);
                 write(") ");
                 if (node.body.kind === SyntaxKind.ModuleBlock) {
                     let saveTempCount = tempCount;
                     let saveTempVariables = tempVariables;
+                    let savePredefinedTempsInUse = predefinedTempsInUse;
                     tempCount = 0;
                     tempVariables = undefined;
-                    let popFrame = enterNameScope();
+                    predefinedTempsInUse = TempVariableKind.auto;
 
                     emit(node.body);
 
-                    exitNameScope(popFrame);
+                    predefinedTempsInUse = savePredefinedTempsInUse;
                     tempCount = saveTempCount;
                     tempVariables = saveTempVariables;
                 }
@@ -3762,7 +3899,7 @@ module ts {
                         }
                         else if (namedImports) {
                             write("var ");
-                            write(resolver.getGeneratedNameForNode(<ImportDeclaration>node));
+                            write(getGeneratedNameForNode(<ImportDeclaration>node));
                             write(" = ");
                             emitRequire(moduleName);
                         }
@@ -3817,7 +3954,7 @@ module ts {
                 if (languageVersion < ScriptTarget.ES6 || node.parent.kind !== SyntaxKind.SourceFile) {
                     if (node.moduleSpecifier) {
                         emitStart(node);
-                        let generatedName = resolver.getGeneratedNameForNode(node);
+                        let generatedName = getGeneratedNameForNode(node);
                         if (compilerOptions.module !== ModuleKind.AMD) {
                             write("var ");
                             write(generatedName);
@@ -3920,7 +4057,7 @@ module ts {
                                 return {
                                     rootNode: <ImportDeclaration>node,
                                     namedImports: <NamedImports>importClause.namedBindings,
-                                    localName: resolver.getGeneratedNameForNode(<ImportDeclaration>node)
+                                    localName: getGeneratedNameForNode(<ImportDeclaration>node)
                                 };
                             }
                         }
@@ -4025,7 +4162,7 @@ module ts {
                         emit(info.declarationNode.name);
                     }
                     else {
-                        write(resolver.getGeneratedNameForNode(<ImportDeclaration | ExportDeclaration>info.rootNode));
+                        write(getGeneratedNameForNode(<ImportDeclaration | ExportDeclaration>info.rootNode));
                     }
                 });
                 forEach(node.amdDependencies, amdDependency => {
diff --git a/src/compiler/types.ts b/src/compiler/types.ts
index 6d0b1309a7280..d2a63a349f908 100644
--- a/src/compiler/types.ts
+++ b/src/compiler/types.ts
@@ -1203,8 +1203,8 @@ module ts {
     }
 
     export interface EmitResolver {
-        getGeneratedNameForNode(node: Node): string;
-        getExpressionNameSubstitution(node: Identifier): string;
+        hasGlobalName(name: string): boolean;
+        getExpressionNameSubstitution(node: Identifier, getGeneratedNameForNode: (node: Node) => string): string;
         hasExportDefaultValue(node: SourceFile): boolean;
         isReferencedAliasDeclaration(node: Node): boolean;
         isTopLevelValueImportEqualsWithEntityName(node: ImportEqualsDeclaration): boolean;
@@ -1219,7 +1219,7 @@ module ts {
         isEntityNameVisible(entityName: EntityName, enclosingDeclaration: Node): SymbolVisibilityResult;
         // Returns the constant value this property access resolves to, or 'undefined' for a non-constant
         getConstantValue(node: EnumMember | PropertyAccessExpression | ElementAccessExpression): number;
-        isUnknownIdentifier(location: Node, name: string): boolean;
+        resolvesToSomeValue(location: Node, name: string): boolean;
         getBlockScopedVariableId(node: Identifier): number;
     }
 
diff --git a/src/compiler/utilities.ts b/src/compiler/utilities.ts
index bdd23f82746b0..a6febeab01665 100644
--- a/src/compiler/utilities.ts
+++ b/src/compiler/utilities.ts
@@ -1212,28 +1212,6 @@ module ts {
         return node;
     }
 
-    export function generateUniqueName(baseName: string, isExistingName: (name: string) => boolean): string {
-        // First try '_name'
-        if (baseName.charCodeAt(0) !== CharacterCodes._) {
-            baseName = "_" + baseName;
-            if (!isExistingName(baseName)) {
-                return baseName;
-            }
-        }
-        // Find the first unique '_name_n', where n is a positive number
-        if (baseName.charCodeAt(baseName.length - 1) !== CharacterCodes._) {
-            baseName += "_";
-        }
-        let i = 1;
-        while (true) {
-            let name = baseName + i;
-            if (!isExistingName(name)) {
-                return name;
-            }
-            i++;
-        }
-    }
-
     // @internal
     export function createDiagnosticCollection(): DiagnosticCollection {
         let nonFileDiagnostics: Diagnostic[] = [];
diff --git a/tests/baselines/reference/APISample_compile.js b/tests/baselines/reference/APISample_compile.js
index b8f4c7cdd136b..cf634849b4403 100644
--- a/tests/baselines/reference/APISample_compile.js
+++ b/tests/baselines/reference/APISample_compile.js
@@ -938,8 +938,8 @@ declare module "typescript" {
         errorModuleName?: string;
     }
     interface EmitResolver {
-        getGeneratedNameForNode(node: Node): string;
-        getExpressionNameSubstitution(node: Identifier): string;
+        hasGlobalName(name: string): boolean;
+        getExpressionNameSubstitution(node: Identifier, getGeneratedNameForNode: (node: Node) => string): string;
         hasExportDefaultValue(node: SourceFile): boolean;
         isReferencedAliasDeclaration(node: Node): boolean;
         isTopLevelValueImportEqualsWithEntityName(node: ImportEqualsDeclaration): boolean;
@@ -953,7 +953,7 @@ declare module "typescript" {
         isSymbolAccessible(symbol: Symbol, enclosingDeclaration: Node, meaning: SymbolFlags): SymbolAccessiblityResult;
         isEntityNameVisible(entityName: EntityName, enclosingDeclaration: Node): SymbolVisibilityResult;
         getConstantValue(node: EnumMember | PropertyAccessExpression | ElementAccessExpression): number;
-        isUnknownIdentifier(location: Node, name: string): boolean;
+        resolvesToSomeValue(location: Node, name: string): boolean;
         getBlockScopedVariableId(node: Identifier): number;
     }
     const enum SymbolFlags {
diff --git a/tests/baselines/reference/APISample_compile.types b/tests/baselines/reference/APISample_compile.types
index e1d9aa5896188..17f393c406a5d 100644
--- a/tests/baselines/reference/APISample_compile.types
+++ b/tests/baselines/reference/APISample_compile.types
@@ -3003,15 +3003,17 @@ declare module "typescript" {
     interface EmitResolver {

 >EmitResolver : EmitResolver
 
-        getGeneratedNameForNode(node: Node): string;

->getGeneratedNameForNode : (node: Node) => string
->node : Node
->Node : Node
+        hasGlobalName(name: string): boolean;

+>hasGlobalName : (name: string) => boolean
+>name : string
 
-        getExpressionNameSubstitution(node: Identifier): string;

->getExpressionNameSubstitution : (node: Identifier) => string
+        getExpressionNameSubstitution(node: Identifier, getGeneratedNameForNode: (node: Node) => string): string;

+>getExpressionNameSubstitution : (node: Identifier, getGeneratedNameForNode: (node: Node) => string) => string
 >node : Identifier
 >Identifier : Identifier
+>getGeneratedNameForNode : (node: Node) => string
+>node : Node
+>Node : Node
 
         hasExportDefaultValue(node: SourceFile): boolean;

 >hasExportDefaultValue : (node: SourceFile) => boolean
@@ -3109,8 +3111,8 @@ declare module "typescript" {
 >PropertyAccessExpression : PropertyAccessExpression
 >ElementAccessExpression : ElementAccessExpression
 
-        isUnknownIdentifier(location: Node, name: string): boolean;

->isUnknownIdentifier : (location: Node, name: string) => boolean
+        resolvesToSomeValue(location: Node, name: string): boolean;

+>resolvesToSomeValue : (location: Node, name: string) => boolean
 >location : Node
 >Node : Node
 >name : string
diff --git a/tests/baselines/reference/APISample_linter.js b/tests/baselines/reference/APISample_linter.js
index 4e3af8d1be096..074db78fd64c9 100644
--- a/tests/baselines/reference/APISample_linter.js
+++ b/tests/baselines/reference/APISample_linter.js
@@ -969,8 +969,8 @@ declare module "typescript" {
         errorModuleName?: string;
     }
     interface EmitResolver {
-        getGeneratedNameForNode(node: Node): string;
-        getExpressionNameSubstitution(node: Identifier): string;
+        hasGlobalName(name: string): boolean;
+        getExpressionNameSubstitution(node: Identifier, getGeneratedNameForNode: (node: Node) => string): string;
         hasExportDefaultValue(node: SourceFile): boolean;
         isReferencedAliasDeclaration(node: Node): boolean;
         isTopLevelValueImportEqualsWithEntityName(node: ImportEqualsDeclaration): boolean;
@@ -984,7 +984,7 @@ declare module "typescript" {
         isSymbolAccessible(symbol: Symbol, enclosingDeclaration: Node, meaning: SymbolFlags): SymbolAccessiblityResult;
         isEntityNameVisible(entityName: EntityName, enclosingDeclaration: Node): SymbolVisibilityResult;
         getConstantValue(node: EnumMember | PropertyAccessExpression | ElementAccessExpression): number;
-        isUnknownIdentifier(location: Node, name: string): boolean;
+        resolvesToSomeValue(location: Node, name: string): boolean;
         getBlockScopedVariableId(node: Identifier): number;
     }
     const enum SymbolFlags {
diff --git a/tests/baselines/reference/APISample_linter.types b/tests/baselines/reference/APISample_linter.types
index 7cf542f0b40f6..46b7c00ab3325 100644
--- a/tests/baselines/reference/APISample_linter.types
+++ b/tests/baselines/reference/APISample_linter.types
@@ -3149,15 +3149,17 @@ declare module "typescript" {
     interface EmitResolver {

 >EmitResolver : EmitResolver
 
-        getGeneratedNameForNode(node: Node): string;

->getGeneratedNameForNode : (node: Node) => string
->node : Node
->Node : Node
+        hasGlobalName(name: string): boolean;

+>hasGlobalName : (name: string) => boolean
+>name : string
 
-        getExpressionNameSubstitution(node: Identifier): string;

->getExpressionNameSubstitution : (node: Identifier) => string
+        getExpressionNameSubstitution(node: Identifier, getGeneratedNameForNode: (node: Node) => string): string;

+>getExpressionNameSubstitution : (node: Identifier, getGeneratedNameForNode: (node: Node) => string) => string
 >node : Identifier
 >Identifier : Identifier
+>getGeneratedNameForNode : (node: Node) => string
+>node : Node
+>Node : Node
 
         hasExportDefaultValue(node: SourceFile): boolean;

 >hasExportDefaultValue : (node: SourceFile) => boolean
@@ -3255,8 +3257,8 @@ declare module "typescript" {
 >PropertyAccessExpression : PropertyAccessExpression
 >ElementAccessExpression : ElementAccessExpression
 
-        isUnknownIdentifier(location: Node, name: string): boolean;

->isUnknownIdentifier : (location: Node, name: string) => boolean
+        resolvesToSomeValue(location: Node, name: string): boolean;

+>resolvesToSomeValue : (location: Node, name: string) => boolean
 >location : Node
 >Node : Node
 >name : string
diff --git a/tests/baselines/reference/APISample_transform.js b/tests/baselines/reference/APISample_transform.js
index 261ad5b25f6fe..ade38f4d1fab4 100644
--- a/tests/baselines/reference/APISample_transform.js
+++ b/tests/baselines/reference/APISample_transform.js
@@ -970,8 +970,8 @@ declare module "typescript" {
         errorModuleName?: string;
     }
     interface EmitResolver {
-        getGeneratedNameForNode(node: Node): string;
-        getExpressionNameSubstitution(node: Identifier): string;
+        hasGlobalName(name: string): boolean;
+        getExpressionNameSubstitution(node: Identifier, getGeneratedNameForNode: (node: Node) => string): string;
         hasExportDefaultValue(node: SourceFile): boolean;
         isReferencedAliasDeclaration(node: Node): boolean;
         isTopLevelValueImportEqualsWithEntityName(node: ImportEqualsDeclaration): boolean;
@@ -985,7 +985,7 @@ declare module "typescript" {
         isSymbolAccessible(symbol: Symbol, enclosingDeclaration: Node, meaning: SymbolFlags): SymbolAccessiblityResult;
         isEntityNameVisible(entityName: EntityName, enclosingDeclaration: Node): SymbolVisibilityResult;
         getConstantValue(node: EnumMember | PropertyAccessExpression | ElementAccessExpression): number;
-        isUnknownIdentifier(location: Node, name: string): boolean;
+        resolvesToSomeValue(location: Node, name: string): boolean;
         getBlockScopedVariableId(node: Identifier): number;
     }
     const enum SymbolFlags {
diff --git a/tests/baselines/reference/APISample_transform.types b/tests/baselines/reference/APISample_transform.types
index eb4c7ab122f89..d1a8e5bff0918 100644
--- a/tests/baselines/reference/APISample_transform.types
+++ b/tests/baselines/reference/APISample_transform.types
@@ -3099,15 +3099,17 @@ declare module "typescript" {
     interface EmitResolver {

 >EmitResolver : EmitResolver
 
-        getGeneratedNameForNode(node: Node): string;

->getGeneratedNameForNode : (node: Node) => string
->node : Node
->Node : Node
+        hasGlobalName(name: string): boolean;

+>hasGlobalName : (name: string) => boolean
+>name : string
 
-        getExpressionNameSubstitution(node: Identifier): string;

->getExpressionNameSubstitution : (node: Identifier) => string
+        getExpressionNameSubstitution(node: Identifier, getGeneratedNameForNode: (node: Node) => string): string;

+>getExpressionNameSubstitution : (node: Identifier, getGeneratedNameForNode: (node: Node) => string) => string
 >node : Identifier
 >Identifier : Identifier
+>getGeneratedNameForNode : (node: Node) => string
+>node : Node
+>Node : Node
 
         hasExportDefaultValue(node: SourceFile): boolean;

 >hasExportDefaultValue : (node: SourceFile) => boolean
@@ -3205,8 +3207,8 @@ declare module "typescript" {
 >PropertyAccessExpression : PropertyAccessExpression
 >ElementAccessExpression : ElementAccessExpression
 
-        isUnknownIdentifier(location: Node, name: string): boolean;

->isUnknownIdentifier : (location: Node, name: string) => boolean
+        resolvesToSomeValue(location: Node, name: string): boolean;

+>resolvesToSomeValue : (location: Node, name: string) => boolean
 >location : Node
 >Node : Node
 >name : string
diff --git a/tests/baselines/reference/APISample_watcher.js b/tests/baselines/reference/APISample_watcher.js
index a821bc5011d74..1b1951af2abb8 100644
--- a/tests/baselines/reference/APISample_watcher.js
+++ b/tests/baselines/reference/APISample_watcher.js
@@ -1007,8 +1007,8 @@ declare module "typescript" {
         errorModuleName?: string;
     }
     interface EmitResolver {
-        getGeneratedNameForNode(node: Node): string;
-        getExpressionNameSubstitution(node: Identifier): string;
+        hasGlobalName(name: string): boolean;
+        getExpressionNameSubstitution(node: Identifier, getGeneratedNameForNode: (node: Node) => string): string;
         hasExportDefaultValue(node: SourceFile): boolean;
         isReferencedAliasDeclaration(node: Node): boolean;
         isTopLevelValueImportEqualsWithEntityName(node: ImportEqualsDeclaration): boolean;
@@ -1022,7 +1022,7 @@ declare module "typescript" {
         isSymbolAccessible(symbol: Symbol, enclosingDeclaration: Node, meaning: SymbolFlags): SymbolAccessiblityResult;
         isEntityNameVisible(entityName: EntityName, enclosingDeclaration: Node): SymbolVisibilityResult;
         getConstantValue(node: EnumMember | PropertyAccessExpression | ElementAccessExpression): number;
-        isUnknownIdentifier(location: Node, name: string): boolean;
+        resolvesToSomeValue(location: Node, name: string): boolean;
         getBlockScopedVariableId(node: Identifier): number;
     }
     const enum SymbolFlags {
diff --git a/tests/baselines/reference/APISample_watcher.types b/tests/baselines/reference/APISample_watcher.types
index 47e5a0147fd00..88a4614e2a44c 100644
--- a/tests/baselines/reference/APISample_watcher.types
+++ b/tests/baselines/reference/APISample_watcher.types
@@ -3272,15 +3272,17 @@ declare module "typescript" {
     interface EmitResolver {

 >EmitResolver : EmitResolver
 
-        getGeneratedNameForNode(node: Node): string;

->getGeneratedNameForNode : (node: Node) => string
->node : Node
->Node : Node
+        hasGlobalName(name: string): boolean;

+>hasGlobalName : (name: string) => boolean
+>name : string
 
-        getExpressionNameSubstitution(node: Identifier): string;

->getExpressionNameSubstitution : (node: Identifier) => string
+        getExpressionNameSubstitution(node: Identifier, getGeneratedNameForNode: (node: Node) => string): string;

+>getExpressionNameSubstitution : (node: Identifier, getGeneratedNameForNode: (node: Node) => string) => string
 >node : Identifier
 >Identifier : Identifier
+>getGeneratedNameForNode : (node: Node) => string
+>node : Node
+>Node : Node
 
         hasExportDefaultValue(node: SourceFile): boolean;

 >hasExportDefaultValue : (node: SourceFile) => boolean
@@ -3378,8 +3380,8 @@ declare module "typescript" {
 >PropertyAccessExpression : PropertyAccessExpression
 >ElementAccessExpression : ElementAccessExpression
 
-        isUnknownIdentifier(location: Node, name: string): boolean;

->isUnknownIdentifier : (location: Node, name: string) => boolean
+        resolvesToSomeValue(location: Node, name: string): boolean;

+>resolvesToSomeValue : (location: Node, name: string) => boolean
 >location : Node
 >Node : Node
 >name : string
diff --git a/tests/baselines/reference/ES5For-of15.js b/tests/baselines/reference/ES5For-of15.js
index 46d3dbd1d6e3e..5a1b8327107c7 100644
--- a/tests/baselines/reference/ES5For-of15.js
+++ b/tests/baselines/reference/ES5For-of15.js
@@ -11,7 +11,7 @@ for (var _i = 0, _a = []; _i < _a.length; _i++) {
     var v = _a[_i];
     v;
     for (var _b = 0, _c = []; _b < _c.length; _b++) {
-        var _v = _c[_b];
-        var x = _v;
+        var v_1 = _c[_b];
+        var x = v_1;
     }
 }
diff --git a/tests/baselines/reference/ES5For-of16.js b/tests/baselines/reference/ES5For-of16.js
index 1649e4481f27d..88f2c39414aa4 100644
--- a/tests/baselines/reference/ES5For-of16.js
+++ b/tests/baselines/reference/ES5For-of16.js
@@ -12,8 +12,8 @@ for (var _i = 0, _a = []; _i < _a.length; _i++) {
     var v = _a[_i];
     v;
     for (var _b = 0, _c = []; _b < _c.length; _b++) {
-        var _v = _c[_b];
-        var x = _v;
-        _v++;
+        var v_1 = _c[_b];
+        var x = v_1;
+        v_1++;
     }
 }
diff --git a/tests/baselines/reference/ES5For-of17.js b/tests/baselines/reference/ES5For-of17.js
index b728074ae939d..4752f1be90f30 100644
--- a/tests/baselines/reference/ES5For-of17.js
+++ b/tests/baselines/reference/ES5For-of17.js
@@ -14,8 +14,8 @@ for (var _i = 0, _a = []; _i < _a.length; _i++) {
     for (var _b = 0, _c = [
         v
     ]; _b < _c.length; _b++) {
-        var _v = _c[_b];
-        var x = _v;
-        _v++;
+        var v_1 = _c[_b];
+        var x = v_1;
+        v_1++;
     }
 }
diff --git a/tests/baselines/reference/ES5For-of18.js b/tests/baselines/reference/ES5For-of18.js
index a135b8b04639e..0d4809ed72d06 100644
--- a/tests/baselines/reference/ES5For-of18.js
+++ b/tests/baselines/reference/ES5For-of18.js
@@ -13,6 +13,6 @@ for (var _i = 0, _a = []; _i < _a.length; _i++) {
     v;
 }
 for (var _b = 0, _c = []; _b < _c.length; _b++) {
-    var _v = _c[_b];
-    _v;
+    var v = _c[_b];
+    v;
 }
diff --git a/tests/baselines/reference/ES5For-of19.js b/tests/baselines/reference/ES5For-of19.js
index 7af9418f04f69..2714574ab5bc8 100644
--- a/tests/baselines/reference/ES5For-of19.js
+++ b/tests/baselines/reference/ES5For-of19.js
@@ -14,9 +14,9 @@ for (var _i = 0, _a = []; _i < _a.length; _i++) {
     var v = _a[_i];
     v;
     function foo() {
-        for (var _b = 0, _c = []; _b < _c.length; _b++) {
-            var _v = _c[_b];
-            _v;
+        for (var _i = 0, _a = []; _i < _a.length; _i++) {
+            var v_1 = _a[_i];
+            v_1;
         }
     }
 }
diff --git a/tests/baselines/reference/ES5For-of20.js b/tests/baselines/reference/ES5For-of20.js
index 3dd707805d8bc..d3f44e4922a1e 100644
--- a/tests/baselines/reference/ES5For-of20.js
+++ b/tests/baselines/reference/ES5For-of20.js
@@ -9,11 +9,11 @@ for (let v of []) {
 //// [ES5For-of20.js]
 for (var _i = 0, _a = []; _i < _a.length; _i++) {
     var v = _a[_i];
-    var _v;
+    var v_1;
     for (var _b = 0, _c = [
         v
     ]; _b < _c.length; _b++) {
-        var _v_1 = _c[_b];
-        var _v_2;
+        var v_2 = _c[_b];
+        var v_3;
     }
 }
diff --git a/tests/baselines/reference/ES5For-of24.js b/tests/baselines/reference/ES5For-of24.js
index 418ccc2005c47..00cd24ea28062 100644
--- a/tests/baselines/reference/ES5For-of24.js
+++ b/tests/baselines/reference/ES5For-of24.js
@@ -12,5 +12,5 @@ var a = [
 ];
 for (var _i = 0; _i < a.length; _i++) {
     var v = a[_i];
-    var _a = 0;
+    var a_1 = 0;
 }
diff --git a/tests/baselines/reference/ModuleWithExportedAndNonExportedClasses.js b/tests/baselines/reference/ModuleWithExportedAndNonExportedClasses.js
index 7555ae217e575..06e5427a87958 100644
--- a/tests/baselines/reference/ModuleWithExportedAndNonExportedClasses.js
+++ b/tests/baselines/reference/ModuleWithExportedAndNonExportedClasses.js
@@ -35,19 +35,19 @@ var ag2 = new A.A2<string, number>();
 
 //// [ModuleWithExportedAndNonExportedClasses.js]
 var A;
-(function (_A) {
+(function (A_1) {
     var A = (function () {
         function A() {
         }
         return A;
     })();
-    _A.A = A;
+    A_1.A = A;
     var AG = (function () {
         function AG() {
         }
         return AG;
     })();
-    _A.AG = AG;
+    A_1.AG = AG;
     var A2 = (function () {
         function A2() {
         }
diff --git a/tests/baselines/reference/cloduleWithRecursiveReference.js b/tests/baselines/reference/cloduleWithRecursiveReference.js
index 1b8a91b3c6817..1a688712270e1 100644
--- a/tests/baselines/reference/cloduleWithRecursiveReference.js
+++ b/tests/baselines/reference/cloduleWithRecursiveReference.js
@@ -17,7 +17,7 @@ var M;
     })();
     M.C = C;
     var C;
-    (function (_C) {
-        _C.C = M.C;
+    (function (C_1) {
+        C_1.C = M.C;
     })(C = M.C || (M.C = {}));
 })(M || (M = {}));
diff --git a/tests/baselines/reference/collisionCodeGenModuleWithAccessorChildren.js b/tests/baselines/reference/collisionCodeGenModuleWithAccessorChildren.js
index 141ef285f037a..8152a9c27215e 100644
--- a/tests/baselines/reference/collisionCodeGenModuleWithAccessorChildren.js
+++ b/tests/baselines/reference/collisionCodeGenModuleWithAccessorChildren.js
@@ -47,14 +47,14 @@ module M { // Shouldnt be _M
 
 //// [collisionCodeGenModuleWithAccessorChildren.js]
 var M;
-(function (_M) {
-    _M.x = 3;
+(function (M_1) {
+    M_1.x = 3;
     var c = (function () {
         function c() {
         }
         Object.defineProperty(c.prototype, "Z", {
             set: function (M) {
-                this.y = _M.x;
+                this.y = M_1.x;
             },
             enumerable: true,
             configurable: true
@@ -63,14 +63,14 @@ var M;
     })();
 })(M || (M = {}));
 var M;
-(function (_M_1) {
+(function (M_2) {
     var d = (function () {
         function d() {
         }
         Object.defineProperty(d.prototype, "Z", {
             set: function (p) {
                 var M = 10;
-                this.y = _M_1.x;
+                this.y = M_2.x;
             },
             enumerable: true,
             configurable: true
@@ -94,14 +94,14 @@ var M;
     })();
 })(M || (M = {}));
 var M;
-(function (_M_2) {
+(function (M_3) {
     var f = (function () {
         function f() {
         }
         Object.defineProperty(f.prototype, "Z", {
             get: function () {
                 var M = 10;
-                return _M_2.x;
+                return M_3.x;
             },
             enumerable: true,
             configurable: true
diff --git a/tests/baselines/reference/collisionCodeGenModuleWithConstructorChildren.js b/tests/baselines/reference/collisionCodeGenModuleWithConstructorChildren.js
index 2158a0562ea2d..2aa705c914123 100644
--- a/tests/baselines/reference/collisionCodeGenModuleWithConstructorChildren.js
+++ b/tests/baselines/reference/collisionCodeGenModuleWithConstructorChildren.js
@@ -25,31 +25,31 @@ module M {
 
 //// [collisionCodeGenModuleWithConstructorChildren.js]
 var M;
-(function (_M) {
-    _M.x = 3;
+(function (M_1) {
+    M_1.x = 3;
     var c = (function () {
         function c(M, p) {
-            if (p === void 0) { p = _M.x; }
+            if (p === void 0) { p = M_1.x; }
         }
         return c;
     })();
 })(M || (M = {}));
 var M;
-(function (_M_1) {
+(function (M_2) {
     var d = (function () {
         function d(M, p) {
-            if (p === void 0) { p = _M_1.x; }
+            if (p === void 0) { p = M_2.x; }
             this.M = M;
         }
         return d;
     })();
 })(M || (M = {}));
 var M;
-(function (_M_2) {
+(function (M_3) {
     var d2 = (function () {
         function d2() {
             var M = 10;
-            var p = _M_2.x;
+            var p = M_3.x;
         }
         return d2;
     })();
diff --git a/tests/baselines/reference/collisionCodeGenModuleWithFunctionChildren.js b/tests/baselines/reference/collisionCodeGenModuleWithFunctionChildren.js
index caaa6a59da525..252ad2c63dc65 100644
--- a/tests/baselines/reference/collisionCodeGenModuleWithFunctionChildren.js
+++ b/tests/baselines/reference/collisionCodeGenModuleWithFunctionChildren.js
@@ -21,24 +21,24 @@ module M {
 
 //// [collisionCodeGenModuleWithFunctionChildren.js]
 var M;
-(function (_M) {
-    _M.x = 3;
+(function (M_1) {
+    M_1.x = 3;
     function fn(M, p) {
-        if (p === void 0) { p = _M.x; }
+        if (p === void 0) { p = M_1.x; }
     }
 })(M || (M = {}));
 var M;
-(function (_M_1) {
+(function (M_2) {
     function fn2() {
         var M;
-        var p = _M_1.x;
+        var p = M_2.x;
     }
 })(M || (M = {}));
 var M;
-(function (_M_2) {
+(function (M_3) {
     function fn3() {
         function M() {
-            var p = _M_2.x;
+            var p = M_3.x;
         }
     }
 })(M || (M = {}));
diff --git a/tests/baselines/reference/collisionCodeGenModuleWithMemberClassConflict.js b/tests/baselines/reference/collisionCodeGenModuleWithMemberClassConflict.js
index 59c2ebf295d52..05ae475e7d234 100644
--- a/tests/baselines/reference/collisionCodeGenModuleWithMemberClassConflict.js
+++ b/tests/baselines/reference/collisionCodeGenModuleWithMemberClassConflict.js
@@ -17,29 +17,29 @@ var foo = new m2._m2();
 
 //// [collisionCodeGenModuleWithMemberClassConflict.js]
 var m1;
-(function (_m1) {
+(function (m1_1) {
     var m1 = (function () {
         function m1() {
         }
         return m1;
     })();
-    _m1.m1 = m1;
+    m1_1.m1 = m1;
 })(m1 || (m1 = {}));
 var foo = new m1.m1();
 var m2;
-(function (_m2_1) {
+(function (m2_1) {
     var m2 = (function () {
         function m2() {
         }
         return m2;
     })();
-    _m2_1.m2 = m2;
+    m2_1.m2 = m2;
     var _m2 = (function () {
         function _m2() {
         }
         return _m2;
     })();
-    _m2_1._m2 = _m2;
+    m2_1._m2 = _m2;
 })(m2 || (m2 = {}));
 var foo = new m2.m2();
 var foo = new m2._m2();
diff --git a/tests/baselines/reference/collisionCodeGenModuleWithMemberVariable.js b/tests/baselines/reference/collisionCodeGenModuleWithMemberVariable.js
index d57de06dfa73d..1a23b81c139e2 100644
--- a/tests/baselines/reference/collisionCodeGenModuleWithMemberVariable.js
+++ b/tests/baselines/reference/collisionCodeGenModuleWithMemberVariable.js
@@ -7,8 +7,8 @@ var foo = m1.m1;
 
 //// [collisionCodeGenModuleWithMemberVariable.js]
 var m1;
-(function (_m1) {
-    _m1.m1 = 10;
-    var b = _m1.m1;
+(function (m1_1) {
+    m1_1.m1 = 10;
+    var b = m1_1.m1;
 })(m1 || (m1 = {}));
 var foo = m1.m1;
diff --git a/tests/baselines/reference/collisionCodeGenModuleWithMethodChildren.js b/tests/baselines/reference/collisionCodeGenModuleWithMethodChildren.js
index 212364ed30b00..53807f1cabd52 100644
--- a/tests/baselines/reference/collisionCodeGenModuleWithMethodChildren.js
+++ b/tests/baselines/reference/collisionCodeGenModuleWithMethodChildren.js
@@ -34,37 +34,37 @@ module M { // Shouldnt bn _M
 
 //// [collisionCodeGenModuleWithMethodChildren.js]
 var M;
-(function (_M) {
-    _M.x = 3;
+(function (M_1) {
+    M_1.x = 3;
     var c = (function () {
         function c() {
         }
         c.prototype.fn = function (M, p) {
-            if (p === void 0) { p = _M.x; }
+            if (p === void 0) { p = M_1.x; }
         };
         return c;
     })();
 })(M || (M = {}));
 var M;
-(function (_M_1) {
+(function (M_2) {
     var d = (function () {
         function d() {
         }
         d.prototype.fn2 = function () {
             var M;
-            var p = _M_1.x;
+            var p = M_2.x;
         };
         return d;
     })();
 })(M || (M = {}));
 var M;
-(function (_M_2) {
+(function (M_3) {
     var e = (function () {
         function e() {
         }
         e.prototype.fn3 = function () {
             function M() {
-                var p = _M_2.x;
+                var p = M_3.x;
             }
         };
         return e;
diff --git a/tests/baselines/reference/collisionCodeGenModuleWithModuleChildren.js b/tests/baselines/reference/collisionCodeGenModuleWithModuleChildren.js
index 3c8b17deadd68..2862a84406786 100644
--- a/tests/baselines/reference/collisionCodeGenModuleWithModuleChildren.js
+++ b/tests/baselines/reference/collisionCodeGenModuleWithModuleChildren.js
@@ -44,16 +44,16 @@ module M {
 
 //// [collisionCodeGenModuleWithModuleChildren.js]
 var M;
-(function (_M) {
-    _M.x = 3;
+(function (M_1) {
+    M_1.x = 3;
     var m1;
     (function (m1) {
         var M = 10;
-        var p = _M.x;
+        var p = M_1.x;
     })(m1 || (m1 = {}));
 })(M || (M = {}));
 var M;
-(function (_M_1) {
+(function (M_2) {
     var m2;
     (function (m2) {
         var M = (function () {
@@ -61,17 +61,17 @@ var M;
             }
             return M;
         })();
-        var p = _M_1.x;
+        var p = M_2.x;
         var p2 = new M();
     })(m2 || (m2 = {}));
 })(M || (M = {}));
 var M;
-(function (_M_2) {
+(function (M_3) {
     var m3;
     (function (m3) {
         function M() {
         }
-        var p = _M_2.x;
+        var p = M_3.x;
         var p2 = M();
     })(m3 || (m3 = {}));
 })(M || (M = {}));
@@ -84,12 +84,12 @@ var M;
     })(m3 || (m3 = {}));
 })(M || (M = {}));
 var M;
-(function (_M_3) {
+(function (M_4) {
     var m4;
     (function (m4) {
         var M;
         (function (M) {
-            var p = _M_3.x;
+            var p = M_4.x;
         })(M || (M = {}));
     })(m4 || (m4 = {}));
 })(M || (M = {}));
diff --git a/tests/baselines/reference/collisionCodeGenModuleWithModuleReopening.js b/tests/baselines/reference/collisionCodeGenModuleWithModuleReopening.js
index 4c3d60230635d..710c09e4558ae 100644
--- a/tests/baselines/reference/collisionCodeGenModuleWithModuleReopening.js
+++ b/tests/baselines/reference/collisionCodeGenModuleWithModuleReopening.js
@@ -31,13 +31,13 @@ var foo2 = new m2.m2();
 
 //// [collisionCodeGenModuleWithModuleReopening.js]
 var m1;
-(function (_m1) {
+(function (m1_1) {
     var m1 = (function () {
         function m1() {
         }
         return m1;
     })();
-    _m1.m1 = m1;
+    m1_1.m1 = m1;
 })(m1 || (m1 = {}));
 var foo = new m1.m1();
 var m1;
@@ -65,16 +65,16 @@ var m2;
 })(m2 || (m2 = {}));
 var foo3 = new m2.c1();
 var m2;
-(function (_m2) {
+(function (m2_1) {
     var m2 = (function () {
         function m2() {
         }
         return m2;
     })();
-    _m2.m2 = m2;
+    m2_1.m2 = m2;
     var b = new m2();
-    var d = _m2.b10;
-    var c = new _m2.c1();
+    var d = m2_1.b10;
+    var c = new m2_1.c1();
 })(m2 || (m2 = {}));
 var foo3 = new m2.c1();
 var foo2 = new m2.m2();
diff --git a/tests/baselines/reference/collisionCodeGenModuleWithPrivateMember.js b/tests/baselines/reference/collisionCodeGenModuleWithPrivateMember.js
index 28901bd11e829..4b4d6aa7afb1b 100644
--- a/tests/baselines/reference/collisionCodeGenModuleWithPrivateMember.js
+++ b/tests/baselines/reference/collisionCodeGenModuleWithPrivateMember.js
@@ -10,7 +10,7 @@ var foo = new m1.c1();
 
 //// [collisionCodeGenModuleWithPrivateMember.js]
 var m1;
-(function (_m1) {
+(function (m1_1) {
     var m1 = (function () {
         function m1() {
         }
@@ -22,6 +22,6 @@ var m1;
         }
         return c1;
     })();
-    _m1.c1 = c1;
+    m1_1.c1 = c1;
 })(m1 || (m1 = {}));
 var foo = new m1.c1();
diff --git a/tests/baselines/reference/collisionCodeGenModuleWithUnicodeNames.js b/tests/baselines/reference/collisionCodeGenModuleWithUnicodeNames.js
index d4e919e0a17ae..3204a05bc7575 100644
--- a/tests/baselines/reference/collisionCodeGenModuleWithUnicodeNames.js
+++ b/tests/baselines/reference/collisionCodeGenModuleWithUnicodeNames.js
@@ -11,12 +11,12 @@ var x = new 才能ソЫⅨ蒤郳र्क्ड्राüışğİliيونيكو
 
 //// [collisionCodeGenModuleWithUnicodeNames.js]
 var 才能ソЫⅨ蒤郳र्क्ड्राüışğİliيونيكودöÄüß才能ソЫⅨ蒤郳र्क्ड्राüışğİliيونيكودöÄüßAbcd123;
-(function (_才能ソЫⅨ蒤郳र्क्ड्राüışğİliيونيكودöÄüß才能ソЫⅨ蒤郳र्क्ड्राüışğİliيونيكودöÄüßAbcd123) {
+(function (才能ソЫⅨ蒤郳र्क्ड्राüışğİliيونيكودöÄüß才能ソЫⅨ蒤郳र्क्ड्राüışğİliيونيكودöÄüßAbcd123_1) {
     var 才能ソЫⅨ蒤郳र्क्ड्राüışğİliيونيكودöÄüß才能ソЫⅨ蒤郳र्क्ड्राüışğİliيونيكودöÄüßAbcd123 = (function () {
         function 才能ソЫⅨ蒤郳र्क्ड्राüışğİliيونيكودöÄüß才能ソЫⅨ蒤郳र्क्ड्राüışğİliيونيكودöÄüßAbcd123() {
         }
         return 才能ソЫⅨ蒤郳र्क्ड्राüışğİliيونيكودöÄüß才能ソЫⅨ蒤郳र्क्ड्राüışğİliيونيكودöÄüßAbcd123;
     })();
-    _才能ソЫⅨ蒤郳र्क्ड्राüışğİliيونيكودöÄüß才能ソЫⅨ蒤郳र्क्ड्राüışğİliيونيكودöÄüßAbcd123.才能ソЫⅨ蒤郳र्क्ड्राüışğİliيونيكودöÄüß才能ソЫⅨ蒤郳र्क्ड्राüışğİliيونيكودöÄüßAbcd123 = 才能ソЫⅨ蒤郳र्क्ड्राüışğİliيونيكودöÄüß才能ソЫⅨ蒤郳र्क्ड्राüışğİliيونيكودöÄüßAbcd123;
+    才能ソЫⅨ蒤郳र्क्ड्राüışğİliيونيكودöÄüß才能ソЫⅨ蒤郳र्क्ड्राüışğİliيونيكودöÄüßAbcd123_1.才能ソЫⅨ蒤郳र्क्ड्राüışğİliيونيكودöÄüß才能ソЫⅨ蒤郳र्क्ड्राüışğİliيونيكودöÄüßAbcd123 = 才能ソЫⅨ蒤郳र्क्ड्राüışğİliيونيكودöÄüß才能ソЫⅨ蒤郳र्क्ड्राüışğİliيونيكودöÄüßAbcd123;
 })(才能ソЫⅨ蒤郳र्क्ड्राüışğİliيونيكودöÄüß才能ソЫⅨ蒤郳र्क्ड्राüışğİliيونيكودöÄüßAbcd123 || (才能ソЫⅨ蒤郳र्क्ड्राüışğİliيونيكودöÄüß才能ソЫⅨ蒤郳र्क्ड्राüışğİliيونيكودöÄüßAbcd123 = {}));
 var x = new 才能ソЫⅨ蒤郳र्क्ड्राüışğİliيونيكودöÄüß才能ソЫⅨ蒤郳र्क्ड्राüışğİliيونيكودöÄüßAbcd123.才能ソЫⅨ蒤郳र्क्ड्राüışğİliيونيكودöÄüß才能ソЫⅨ蒤郳र्क्ड्राüışğİliيونيكودöÄüßAbcd123();
diff --git a/tests/baselines/reference/declFileImportChainInExportAssignment.js b/tests/baselines/reference/declFileImportChainInExportAssignment.js
index c8773889a7d0b..4ec3893d02fa8 100644
--- a/tests/baselines/reference/declFileImportChainInExportAssignment.js
+++ b/tests/baselines/reference/declFileImportChainInExportAssignment.js
@@ -13,13 +13,13 @@ export = b;
 var m;
 (function (m) {
     var c;
-    (function (_c) {
+    (function (c_1) {
         var c = (function () {
             function c() {
             }
             return c;
         })();
-        _c.c = c;
+        c_1.c = c;
     })(c = m.c || (m.c = {}));
 })(m || (m = {}));
 var a = m.c;
diff --git a/tests/baselines/reference/declarationEmitDestructuringObjectLiteralPattern.js b/tests/baselines/reference/declarationEmitDestructuringObjectLiteralPattern.js
index de3045be1ccc5..9b48f418f5ad5 100644
--- a/tests/baselines/reference/declarationEmitDestructuringObjectLiteralPattern.js
+++ b/tests/baselines/reference/declarationEmitDestructuringObjectLiteralPattern.js
@@ -73,8 +73,8 @@ function f15() {
 var _f = f15(), a4 = _f.a4, b4 = _f.b4, c4 = _f.c4;
 var m;
 (function (m) {
-    _g = f15(), m.a4 = _g.a4, m.b4 = _g.b4, m.c4 = _g.c4;
-    var _g;
+    _a = f15(), m.a4 = _a.a4, m.b4 = _a.b4, m.c4 = _a.c4;
+    var _a;
 })(m || (m = {}));
 
 
diff --git a/tests/baselines/reference/declarationEmitDestructuringObjectLiteralPattern2.js b/tests/baselines/reference/declarationEmitDestructuringObjectLiteralPattern2.js
index 509edfa6c87f1..140fc03780a05 100644
--- a/tests/baselines/reference/declarationEmitDestructuringObjectLiteralPattern2.js
+++ b/tests/baselines/reference/declarationEmitDestructuringObjectLiteralPattern2.js
@@ -37,8 +37,8 @@ function f15() {
 var _c = f15(), a4 = _c.a4, b4 = _c.b4, c4 = _c.c4;
 var m;
 (function (m) {
-    _d = f15(), m.a4 = _d.a4, m.b4 = _d.b4, m.c4 = _d.c4;
-    var _d;
+    _a = f15(), m.a4 = _a.a4, m.b4 = _a.b4, m.c4 = _a.c4;
+    var _a;
 })(m || (m = {}));
 
 
diff --git a/tests/baselines/reference/declarationEmitImportInExportAssignmentModule.js b/tests/baselines/reference/declarationEmitImportInExportAssignmentModule.js
index b41ca177b0558..9b580bcd7a4e3 100644
--- a/tests/baselines/reference/declarationEmitImportInExportAssignmentModule.js
+++ b/tests/baselines/reference/declarationEmitImportInExportAssignmentModule.js
@@ -14,13 +14,13 @@ export = m;
 var m;
 (function (m) {
     var c;
-    (function (_c) {
+    (function (c_1) {
         var c = (function () {
             function c() {
             }
             return c;
         })();
-        _c.c = c;
+        c_1.c = c;
     })(c = m.c || (m.c = {}));
     m.a;
 })(m || (m = {}));
diff --git a/tests/baselines/reference/downlevelLetConst14.js b/tests/baselines/reference/downlevelLetConst14.js
index ffe667eda3f4c..ac9444f9facca 100644
--- a/tests/baselines/reference/downlevelLetConst14.js
+++ b/tests/baselines/reference/downlevelLetConst14.js
@@ -59,24 +59,24 @@ use(y);
 var x = 10;
 var z0, z1, z2, z3;
 {
-    var _x = 20;
-    use(_x);
-    var _z0 = ([
+    var x_1 = 20;
+    use(x_1);
+    var z0_1 = ([
         1
     ])[0];
-    use(_z0);
-    var _z1 = ([
+    use(z0_1);
+    var z1_1 = ([
         1
     ])[0];
-    use(_z1);
-    var _z2 = ({
+    use(z1_1);
+    var z2_1 = ({
         a: 1
     }).a;
-    use(_z2);
-    var _z3 = ({
+    use(z2_1);
+    var z3_1 = ({
         a: 1
     }).a;
-    use(_z3);
+    use(z3_1);
 }
 use(x);
 use(z0);
@@ -86,38 +86,38 @@ use(z3);
 var z6;
 var y = true;
 {
-    var _y = "";
-    var _z6 = ([
+    var y_1 = "";
+    var z6_1 = ([
         true
     ])[0];
     {
-        var _y_1 = 1;
-        var _z6_1 = ({
+        var y_2 = 1;
+        var z6_2 = ({
             a: 1
         }).a;
-        use(_y_1);
-        use(_z6_1);
+        use(y_2);
+        use(z6_2);
     }
-    use(_y);
-    use(_z6);
+    use(y_1);
+    use(z6_1);
 }
 use(y);
 use(z6);
 var z = false;
 var z5 = 1;
 {
-    var _z = "";
-    var _z5 = ([
+    var z_1 = "";
+    var z5_1 = ([
         5
     ])[0];
     {
-        var _z_1 = 1;
-        var _z5_1 = ({
+        var _z = 1;
+        var _z5 = ({
             a: 1
         }).a;
         // try to step on generated name
-        use(_z_1);
+        use(_z);
     }
-    use(_z);
+    use(z_1);
 }
 use(y);
diff --git a/tests/baselines/reference/downlevelLetConst15.js b/tests/baselines/reference/downlevelLetConst15.js
index 94fcb1b03a008..f1b476c017612 100644
--- a/tests/baselines/reference/downlevelLetConst15.js
+++ b/tests/baselines/reference/downlevelLetConst15.js
@@ -59,28 +59,28 @@ use(y);
 var x = 10;
 var z0, z1, z2, z3;
 {
-    var _x = 20;
-    use(_x);
-    var _z0 = ([
+    var x_1 = 20;
+    use(x_1);
+    var z0_1 = ([
         1
     ])[0];
-    use(_z0);
-    var _z1 = ([
+    use(z0_1);
+    var z1_1 = ([
         {
             a: 1
         }
     ])[0].a;
-    use(_z1);
-    var _z2 = ({
+    use(z1_1);
+    var z2_1 = ({
         a: 1
     }).a;
-    use(_z2);
-    var _z3 = ({
+    use(z2_1);
+    var z3_1 = ({
         a: {
             b: 1
         }
     }).a.b;
-    use(_z3);
+    use(z3_1);
 }
 use(x);
 use(z0);
@@ -90,38 +90,38 @@ use(z3);
 var z6;
 var y = true;
 {
-    var _y = "";
-    var _z6 = ([
+    var y_1 = "";
+    var z6_1 = ([
         true
     ])[0];
     {
-        var _y_1 = 1;
-        var _z6_1 = ({
+        var y_2 = 1;
+        var z6_2 = ({
             a: 1
         }).a;
-        use(_y_1);
-        use(_z6_1);
+        use(y_2);
+        use(z6_2);
     }
-    use(_y);
-    use(_z6);
+    use(y_1);
+    use(z6_1);
 }
 use(y);
 use(z6);
 var z = false;
 var z5 = 1;
 {
-    var _z = "";
-    var _z5 = ([
+    var z_1 = "";
+    var z5_1 = ([
         5
     ])[0];
     {
-        var _z_1 = 1;
-        var _z5_1 = ({
+        var _z = 1;
+        var _z5 = ({
             a: 1
         }).a;
         // try to step on generated name
-        use(_z_1);
+        use(_z);
     }
-    use(_z);
+    use(z_1);
 }
 use(y);
diff --git a/tests/baselines/reference/downlevelLetConst16.js b/tests/baselines/reference/downlevelLetConst16.js
index f83e745c55403..aefe2830adc2f 100644
--- a/tests/baselines/reference/downlevelLetConst16.js
+++ b/tests/baselines/reference/downlevelLetConst16.js
@@ -236,29 +236,29 @@ use(x);
 use(y);
 use(z);
 function foo1() {
-    var _x = 1;
-    use(_x);
-    var _y = ([
+    var x = 1;
+    use(x);
+    var y = ([
         1
     ])[0];
-    use(_y);
-    var _z = ({
+    use(y);
+    var z = ({
         a: 1
     }).a;
-    use(_z);
+    use(z);
 }
 function foo2() {
     {
-        var _x = 1;
-        use(_x);
-        var _y = ([
+        var x_1 = 1;
+        use(x_1);
+        var y_1 = ([
             1
         ])[0];
-        use(_y);
-        var _z = ({
+        use(y_1);
+        var z_1 = ({
             a: 1
         }).a;
-        use(_z);
+        use(z_1);
     }
     use(x);
 }
@@ -266,29 +266,29 @@ var A = (function () {
     function A() {
     }
     A.prototype.m1 = function () {
-        var _x = 1;
-        use(_x);
-        var _y = ([
+        var x = 1;
+        use(x);
+        var y = ([
             1
         ])[0];
-        use(_y);
-        var _z = ({
+        use(y);
+        var z = ({
             a: 1
         }).a;
-        use(_z);
+        use(z);
     };
     A.prototype.m2 = function () {
         {
-            var _x = 1;
-            use(_x);
-            var _y = ([
+            var x_2 = 1;
+            use(x_2);
+            var y_2 = ([
                 1
             ])[0];
-            use(_y);
-            var _z = ({
+            use(y_2);
+            var z_2 = ({
                 a: 1
             }).a;
-            use(_z);
+            use(z_2);
         }
         use(x);
     };
@@ -298,200 +298,200 @@ var B = (function () {
     function B() {
     }
     B.prototype.m1 = function () {
-        var _x = 1;
-        use(_x);
-        var _y = ([
+        var x = 1;
+        use(x);
+        var y = ([
             1
         ])[0];
-        use(_y);
-        var _z = ({
+        use(y);
+        var z = ({
             a: 1
         }).a;
-        use(_z);
+        use(z);
     };
     B.prototype.m2 = function () {
         {
-            var _x = 1;
-            use(_x);
-            var _y = ([
+            var x_3 = 1;
+            use(x_3);
+            var y_3 = ([
                 1
             ])[0];
-            use(_y);
-            var _z = ({
+            use(y_3);
+            var z_3 = ({
                 a: 1
             }).a;
-            use(_z);
+            use(z_3);
         }
         use(x);
     };
     return B;
 })();
 function bar1() {
-    var _x = 1;
-    use(_x);
-    var _y = ([
+    var x = 1;
+    use(x);
+    var y = ([
         1
     ])[0];
-    use(_y);
-    var _z = ({
+    use(y);
+    var z = ({
         a: 1
     }).a;
-    use(_z);
+    use(z);
 }
 function bar2() {
     {
-        var _x = 1;
-        use(_x);
-        var _y = ([
+        var x_4 = 1;
+        use(x_4);
+        var y_4 = ([
             1
         ])[0];
-        use(_y);
-        var _z = ({
+        use(y_4);
+        var z_4 = ({
             a: 1
         }).a;
-        use(_z);
+        use(z_4);
     }
     use(x);
 }
 var M1;
 (function (M1) {
-    var _x = 1;
-    use(_x);
-    var _y = ([
+    var x = 1;
+    use(x);
+    var y = ([
         1
     ])[0];
-    use(_y);
-    var _z = ({
+    use(y);
+    var z = ({
         a: 1
     }).a;
-    use(_z);
+    use(z);
 })(M1 || (M1 = {}));
 var M2;
 (function (M2) {
     {
-        var _x = 1;
-        use(_x);
-        var _y = ([
+        var x_5 = 1;
+        use(x_5);
+        var y_5 = ([
             1
         ])[0];
-        use(_y);
-        var _z = ({
+        use(y_5);
+        var z_5 = ({
             a: 1
         }).a;
-        use(_z);
+        use(z_5);
     }
     use(x);
 })(M2 || (M2 = {}));
 var M3;
 (function (M3) {
-    var _x = 1;
-    use(_x);
-    var _y = ([
+    var x = 1;
+    use(x);
+    var y = ([
         1
     ])[0];
-    use(_y);
-    var _z = ({
+    use(y);
+    var z = ({
         a: 1
     }).a;
-    use(_z);
+    use(z);
 })(M3 || (M3 = {}));
 var M4;
 (function (M4) {
     {
-        var _x = 1;
-        use(_x);
-        var _y = ([
+        var x_6 = 1;
+        use(x_6);
+        var y_6 = ([
             1
         ])[0];
-        use(_y);
-        var _z = ({
+        use(y_6);
+        var z_6 = ({
             a: 1
         }).a;
-        use(_z);
+        use(z_6);
     }
     use(x);
     use(y);
     use(z);
 })(M4 || (M4 = {}));
 function foo3() {
-    for (var _x = void 0;;) {
-        use(_x);
+    for (var x_7 = void 0;;) {
+        use(x_7);
     }
-    for (var _y = ([])[0];;) {
-        use(_y);
+    for (var y_7 = ([])[0];;) {
+        use(y_7);
     }
-    for (var _z = ({
+    for (var z_7 = ({
         a: 1
     }).a;;) {
-        use(_z);
+        use(z_7);
     }
     use(x);
 }
 function foo4() {
-    for (var _x = 1;;) {
-        use(_x);
+    for (var x_8 = 1;;) {
+        use(x_8);
     }
-    for (var _y = ([])[0];;) {
-        use(_y);
+    for (var y_8 = ([])[0];;) {
+        use(y_8);
     }
-    for (var _z = ({
+    for (var z_8 = ({
         a: 1
     }).a;;) {
-        use(_z);
+        use(z_8);
     }
     use(x);
 }
 function foo5() {
-    for (var _x in []) {
-        use(_x);
+    for (var x_9 in []) {
+        use(x_9);
     }
     use(x);
 }
 function foo6() {
-    for (var _x in []) {
-        use(_x);
+    for (var x_10 in []) {
+        use(x_10);
     }
     use(x);
 }
 function foo7() {
     for (var _i = 0, _a = []; _i < _a.length; _i++) {
-        var _x = _a[_i];
-        use(_x);
+        var x_11 = _a[_i];
+        use(x_11);
     }
     use(x);
 }
 function foo8() {
     for (var _i = 0, _a = []; _i < _a.length; _i++) {
-        var _x = _a[_i][0];
-        use(_x);
+        var x_12 = _a[_i][0];
+        use(x_12);
     }
     use(x);
 }
 function foo9() {
     for (var _i = 0, _a = []; _i < _a.length; _i++) {
-        var _x = _a[_i].a;
-        use(_x);
+        var x_13 = _a[_i].a;
+        use(x_13);
     }
     use(x);
 }
 function foo10() {
     for (var _i = 0, _a = []; _i < _a.length; _i++) {
-        var _x = _a[_i];
-        use(_x);
+        var x_14 = _a[_i];
+        use(x_14);
     }
     use(x);
 }
 function foo11() {
     for (var _i = 0, _a = []; _i < _a.length; _i++) {
-        var _x = _a[_i][0];
-        use(_x);
+        var x_15 = _a[_i][0];
+        use(x_15);
     }
     use(x);
 }
 function foo12() {
     for (var _i = 0, _a = []; _i < _a.length; _i++) {
-        var _x = _a[_i].a;
-        use(_x);
+        var x_16 = _a[_i].a;
+        use(x_16);
     }
     use(x);
 }
diff --git a/tests/baselines/reference/downlevelLetConst17.js b/tests/baselines/reference/downlevelLetConst17.js
index d38ec3fde08c8..56ab1e6df54c6 100644
--- a/tests/baselines/reference/downlevelLetConst17.js
+++ b/tests/baselines/reference/downlevelLetConst17.js
@@ -70,54 +70,54 @@ for (const x of []) {
 //// [downlevelLetConst17.js]
 'use strict';
 var x;
-for (var _x = 10;;) {
-    use(_x);
+for (var x_1 = 10;;) {
+    use(x_1);
 }
 use(x);
-for (var _x_1 = 10;;) {
-    use(_x_1);
+for (var x_2 = 10;;) {
+    use(x_2);
 }
 for (;;) {
-    var _x_2 = 10;
-    use(_x_2);
-    _x_2 = 1;
+    var x_3 = 10;
+    use(x_3);
+    x_3 = 1;
 }
 for (;;) {
-    var _x_3 = 10;
-    use(_x_3);
+    var x_4 = 10;
+    use(x_4);
 }
-for (var _x_4 = void 0;;) {
-    use(_x_4);
-    _x_4 = 1;
+for (var x_5 = void 0;;) {
+    use(x_5);
+    x_5 = 1;
 }
 for (;;) {
-    var _x_5 = void 0;
-    use(_x_5);
-    _x_5 = 1;
+    var x_6 = void 0;
+    use(x_6);
+    x_6 = 1;
 }
 while (true) {
-    var _x_6 = void 0;
-    use(_x_6);
+    var x_7 = void 0;
+    use(x_7);
 }
 while (true) {
-    var _x_7 = true;
-    use(_x_7);
+    var x_8 = true;
+    use(x_8);
 }
 do {
-    var _x_8 = void 0;
-    use(_x_8);
+    var x_9 = void 0;
+    use(x_9);
 } while (true);
 do {
-    var _x_9 = void 0;
-    use(_x_9);
+    var x_10 = void 0;
+    use(x_10);
 } while (true);
-for (var _x_10 in []) {
-    use(_x_10);
+for (var x_11 in []) {
+    use(x_11);
 }
-for (var _x_11 in []) {
-    use(_x_11);
+for (var x_12 in []) {
+    use(x_12);
 }
 for (var _i = 0, _a = []; _i < _a.length; _i++) {
-    var _x_12 = _a[_i];
-    use(_x_12);
+    var x_13 = _a[_i];
+    use(x_13);
 }
diff --git a/tests/baselines/reference/downlevelLetConst18.js b/tests/baselines/reference/downlevelLetConst18.js
index 0c025573e209b..f3b2306d62b33 100644
--- a/tests/baselines/reference/downlevelLetConst18.js
+++ b/tests/baselines/reference/downlevelLetConst18.js
@@ -38,40 +38,40 @@ for (var x = void 0;;) {
     }
     ;
 }
-for (var _x = void 0;;) {
+for (var x = void 0;;) {
     function foo() {
-        _x;
+        x;
     }
     ;
 }
-for (var _x_1 = void 0;;) {
+for (var x = void 0;;) {
     (function () {
-        _x_1;
+        x;
     })();
 }
-for (var _x_2 = 1;;) {
+for (var x = 1;;) {
     (function () {
-        _x_2;
+        x;
     })();
 }
-for (var _x_3 = void 0;;) {
+for (var x = void 0;;) {
     ({
         foo: function () {
-            _x_3;
+            x;
         }
     });
 }
-for (var _x_4 = void 0;;) {
+for (var x = void 0;;) {
     ({
         get foo() {
-            return _x_4;
+            return x;
         }
     });
 }
-for (var _x_5 = void 0;;) {
+for (var x = void 0;;) {
     ({
         set foo(v) {
-            _x_5;
+            x;
         }
     });
 }
diff --git a/tests/baselines/reference/downlevelLetConst19.js b/tests/baselines/reference/downlevelLetConst19.js
index adcc2e256a81d..2b3ec8036cbdb 100644
--- a/tests/baselines/reference/downlevelLetConst19.js
+++ b/tests/baselines/reference/downlevelLetConst19.js
@@ -24,14 +24,14 @@ use(x)
 var x;
 function a() {
     {
-        var _x;
-        use(_x);
+        var x_1;
+        use(x_1);
         function b() {
             {
-                var _x_1;
-                use(_x_1);
+                var x_2;
+                use(x_2);
             }
-            use(_x);
+            use(x_1);
         }
     }
     use(x);
diff --git a/tests/baselines/reference/duplicateExportAssignments.js b/tests/baselines/reference/duplicateExportAssignments.js
index 7d2776962f7ad..3742a5f1fe54f 100644
--- a/tests/baselines/reference/duplicateExportAssignments.js
+++ b/tests/baselines/reference/duplicateExportAssignments.js
@@ -56,8 +56,8 @@ var y = (function () {
 module.exports = x;
 //// [foo3.js]
 var x;
-(function (_x) {
-    _x.x = 10;
+(function (x_1) {
+    x_1.x = 10;
 })(x || (x = {}));
 var y = (function () {
     function y() {
diff --git a/tests/baselines/reference/es5ExportDefaultClassDeclaration2.js b/tests/baselines/reference/es5ExportDefaultClassDeclaration2.js
index 3e4e4d9eed692..6687d8dd2d98c 100644
--- a/tests/baselines/reference/es5ExportDefaultClassDeclaration2.js
+++ b/tests/baselines/reference/es5ExportDefaultClassDeclaration2.js
@@ -6,14 +6,14 @@ export default class {
 
 
 //// [es5ExportDefaultClassDeclaration2.js]
-var _default = (function () {
-    function _default() {
+var default_1 = (function () {
+    function default_1() {
     }
-    _default.prototype.method = function () {
+    default_1.prototype.method = function () {
     };
-    return _default;
+    return default_1;
 })();
-module.exports = _default;
+module.exports = default_1;
 
 
 //// [es5ExportDefaultClassDeclaration2.d.ts]
diff --git a/tests/baselines/reference/es5ExportDefaultFunctionDeclaration2.js b/tests/baselines/reference/es5ExportDefaultFunctionDeclaration2.js
index dedb36b7e643f..696efe5fbb14f 100644
--- a/tests/baselines/reference/es5ExportDefaultFunctionDeclaration2.js
+++ b/tests/baselines/reference/es5ExportDefaultFunctionDeclaration2.js
@@ -6,7 +6,7 @@ export default function () { }
 //// [es5ExportDefaultFunctionDeclaration2.js]
 function () {
 }
-module.exports = _default;
+module.exports = default_1;
 
 
 //// [es5ExportDefaultFunctionDeclaration2.d.ts]
diff --git a/tests/baselines/reference/es6ExportAllInEs5.js b/tests/baselines/reference/es6ExportAllInEs5.js
index dd83c31b72a7f..073fbdaab38ed 100644
--- a/tests/baselines/reference/es6ExportAllInEs5.js
+++ b/tests/baselines/reference/es6ExportAllInEs5.js
@@ -29,8 +29,8 @@ var m;
 })(m = exports.m || (exports.m = {}));
 exports.x = 10;
 //// [client.js]
-var _server = require("server");
-for (var _a in _server) if (!exports.hasOwnProperty(_a)) exports[_a] = _server[_a];
+var server_1 = require("server");
+for (var _a in server_1) if (!exports.hasOwnProperty(_a)) exports[_a] = server_1[_a];
 
 
 //// [server.d.ts]
diff --git a/tests/baselines/reference/es6ExportClauseWithoutModuleSpecifierInEs5.js b/tests/baselines/reference/es6ExportClauseWithoutModuleSpecifierInEs5.js
index 3e412c13a329a..2bc573ce77f9e 100644
--- a/tests/baselines/reference/es6ExportClauseWithoutModuleSpecifierInEs5.js
+++ b/tests/baselines/reference/es6ExportClauseWithoutModuleSpecifierInEs5.js
@@ -33,17 +33,17 @@ var m;
 })(m = exports.m || (exports.m = {}));
 exports.x = 10;
 //// [client.js]
-var _server = require("server");
-exports.c = _server.c;
-var _server_1 = require("server");
-exports.c2 = _server_1.c;
-var _server_2 = require("server");
-exports.i = _server_2.i;
-exports.instantiatedModule = _server_2.m;
-var _server_3 = require("server");
-exports.uninstantiated = _server_3.uninstantiated;
-var _server_4 = require("server");
-exports.x = _server_4.x;
+var server_1 = require("server");
+exports.c = server_1.c;
+var server_2 = require("server");
+exports.c2 = server_2.c;
+var server_3 = require("server");
+exports.i = server_3.i;
+exports.instantiatedModule = server_3.m;
+var server_4 = require("server");
+exports.uninstantiated = server_4.uninstantiated;
+var server_5 = require("server");
+exports.x = server_5.x;
 
 
 //// [server.d.ts]
diff --git a/tests/baselines/reference/es6ImportDefaultBindingFollowedWithNamedImportDts.js b/tests/baselines/reference/es6ImportDefaultBindingFollowedWithNamedImportDts.js
index 6c85e281150de..8cf9ab1ffb129 100644
--- a/tests/baselines/reference/es6ImportDefaultBindingFollowedWithNamedImportDts.js
+++ b/tests/baselines/reference/es6ImportDefaultBindingFollowedWithNamedImportDts.js
@@ -62,17 +62,17 @@ var x11 = (function () {
 })();
 exports.x11 = x11;
 //// [client.js]
-var _server_1 = require("server");
-exports.x1 = new _server_1.a();
-var _server_2 = require("server");
-exports.x2 = new _server_2.a11();
-var _server_3 = require("server");
-exports.x4 = new _server_3.x();
-exports.x5 = new _server_3.a12();
-var _server_4 = require("server");
-exports.x3 = new _server_4.x11();
-var _server_5 = require("server");
-exports.x6 = new _server_5.m();
+var server_1 = require("server");
+exports.x1 = new server_1.a();
+var server_2 = require("server");
+exports.x2 = new server_2.a11();
+var server_3 = require("server");
+exports.x4 = new server_3.x();
+exports.x5 = new server_3.a12();
+var server_4 = require("server");
+exports.x3 = new server_4.x11();
+var server_5 = require("server");
+exports.x6 = new server_5.m();
 
 
 //// [server.d.ts]
diff --git a/tests/baselines/reference/es6ImportDefaultBindingFollowedWithNamedImportInEs5.js b/tests/baselines/reference/es6ImportDefaultBindingFollowedWithNamedImportInEs5.js
index 1c63005bb0680..1c65fadbe1d43 100644
--- a/tests/baselines/reference/es6ImportDefaultBindingFollowedWithNamedImportInEs5.js
+++ b/tests/baselines/reference/es6ImportDefaultBindingFollowedWithNamedImportInEs5.js
@@ -26,17 +26,17 @@ exports.a = 10;
 exports.x = exports.a;
 exports.m = exports.a;
 //// [es6ImportDefaultBindingFollowedWithNamedImportInEs5_1.js]
-var _es6ImportDefaultBindingFollowedWithNamedImportInEs5_0_1 = require("es6ImportDefaultBindingFollowedWithNamedImportInEs5_0");
-var x1 = _es6ImportDefaultBindingFollowedWithNamedImportInEs5_0_1.a;
-var _es6ImportDefaultBindingFollowedWithNamedImportInEs5_0_2 = require("es6ImportDefaultBindingFollowedWithNamedImportInEs5_0");
-var x1 = _es6ImportDefaultBindingFollowedWithNamedImportInEs5_0_2.a;
-var _es6ImportDefaultBindingFollowedWithNamedImportInEs5_0_3 = require("es6ImportDefaultBindingFollowedWithNamedImportInEs5_0");
-var x1 = _es6ImportDefaultBindingFollowedWithNamedImportInEs5_0_3.x;
-var x1 = _es6ImportDefaultBindingFollowedWithNamedImportInEs5_0_3.a;
-var _es6ImportDefaultBindingFollowedWithNamedImportInEs5_0_4 = require("es6ImportDefaultBindingFollowedWithNamedImportInEs5_0");
-var x1 = _es6ImportDefaultBindingFollowedWithNamedImportInEs5_0_4.x;
-var _es6ImportDefaultBindingFollowedWithNamedImportInEs5_0_5 = require("es6ImportDefaultBindingFollowedWithNamedImportInEs5_0");
-var x1 = _es6ImportDefaultBindingFollowedWithNamedImportInEs5_0_5.m;
+var es6ImportDefaultBindingFollowedWithNamedImportInEs5_0_1 = require("es6ImportDefaultBindingFollowedWithNamedImportInEs5_0");
+var x1 = es6ImportDefaultBindingFollowedWithNamedImportInEs5_0_1.a;
+var es6ImportDefaultBindingFollowedWithNamedImportInEs5_0_2 = require("es6ImportDefaultBindingFollowedWithNamedImportInEs5_0");
+var x1 = es6ImportDefaultBindingFollowedWithNamedImportInEs5_0_2.a;
+var es6ImportDefaultBindingFollowedWithNamedImportInEs5_0_3 = require("es6ImportDefaultBindingFollowedWithNamedImportInEs5_0");
+var x1 = es6ImportDefaultBindingFollowedWithNamedImportInEs5_0_3.x;
+var x1 = es6ImportDefaultBindingFollowedWithNamedImportInEs5_0_3.a;
+var es6ImportDefaultBindingFollowedWithNamedImportInEs5_0_4 = require("es6ImportDefaultBindingFollowedWithNamedImportInEs5_0");
+var x1 = es6ImportDefaultBindingFollowedWithNamedImportInEs5_0_4.x;
+var es6ImportDefaultBindingFollowedWithNamedImportInEs5_0_5 = require("es6ImportDefaultBindingFollowedWithNamedImportInEs5_0");
+var x1 = es6ImportDefaultBindingFollowedWithNamedImportInEs5_0_5.m;
 
 
 //// [es6ImportDefaultBindingFollowedWithNamedImportInEs5_0.d.ts]
diff --git a/tests/baselines/reference/es6ImportDefaultBindingFollowedWithNamedImportWithExport.js b/tests/baselines/reference/es6ImportDefaultBindingFollowedWithNamedImportWithExport.js
index 5497a82b04151..af73279126f61 100644
--- a/tests/baselines/reference/es6ImportDefaultBindingFollowedWithNamedImportWithExport.js
+++ b/tests/baselines/reference/es6ImportDefaultBindingFollowedWithNamedImportWithExport.js
@@ -28,13 +28,13 @@ define(["require", "exports"], function (require, exports) {
     exports.m = exports.a;
 });
 //// [client.js]
-define(["require", "exports", "server", "server", "server", "server", "server"], function (require, exports, _server_1, _server_2, _server_3, _server_4, _server_5) {
-    exports.x1 = _server_1.a;
-    exports.x1 = _server_2.a;
-    exports.x1 = _server_3.x;
-    exports.x1 = _server_3.a;
-    exports.x1 = _server_4.x;
-    exports.x1 = _server_5.m;
+define(["require", "exports", "server", "server", "server", "server", "server"], function (require, exports, server_1, server_2, server_3, server_4, server_5) {
+    exports.x1 = server_1.a;
+    exports.x1 = server_2.a;
+    exports.x1 = server_3.x;
+    exports.x1 = server_3.a;
+    exports.x1 = server_4.x;
+    exports.x1 = server_5.m;
 });
 
 
diff --git a/tests/baselines/reference/es6ImportNamedImportAmd.js b/tests/baselines/reference/es6ImportNamedImportAmd.js
index 5e3ddc433083a..c335337325e51 100644
--- a/tests/baselines/reference/es6ImportNamedImportAmd.js
+++ b/tests/baselines/reference/es6ImportNamedImportAmd.js
@@ -53,19 +53,19 @@ define(["require", "exports"], function (require, exports) {
     exports.aaaa = 10;
 });
 //// [es6ImportNamedImportAmd_1.js]
-define(["require", "exports", "es6ImportNamedImportAmd_0", "es6ImportNamedImportAmd_0", "es6ImportNamedImportAmd_0", "es6ImportNamedImportAmd_0", "es6ImportNamedImportAmd_0", "es6ImportNamedImportAmd_0", "es6ImportNamedImportAmd_0", "es6ImportNamedImportAmd_0", "es6ImportNamedImportAmd_0"], function (require, exports, _es6ImportNamedImportAmd_0_1, _es6ImportNamedImportAmd_0_2, _es6ImportNamedImportAmd_0_3, _es6ImportNamedImportAmd_0_4, _es6ImportNamedImportAmd_0_5, _es6ImportNamedImportAmd_0_6, _es6ImportNamedImportAmd_0_7, _es6ImportNamedImportAmd_0_8, _es6ImportNamedImportAmd_0_9) {
-    var xxxx = _es6ImportNamedImportAmd_0_1.a;
-    var xxxx = _es6ImportNamedImportAmd_0_2.a;
-    var xxxx = _es6ImportNamedImportAmd_0_3.x;
-    var xxxx = _es6ImportNamedImportAmd_0_3.a;
-    var xxxx = _es6ImportNamedImportAmd_0_4.x;
-    var xxxx = _es6ImportNamedImportAmd_0_5.m;
-    var xxxx = _es6ImportNamedImportAmd_0_6.a1;
-    var xxxx = _es6ImportNamedImportAmd_0_6.x1;
-    var xxxx = _es6ImportNamedImportAmd_0_7.a1;
-    var xxxx = _es6ImportNamedImportAmd_0_7.x1;
-    var z111 = _es6ImportNamedImportAmd_0_8.z1;
-    var z2 = _es6ImportNamedImportAmd_0_9.z2; // z2 shouldn't give redeclare error
+define(["require", "exports", "es6ImportNamedImportAmd_0", "es6ImportNamedImportAmd_0", "es6ImportNamedImportAmd_0", "es6ImportNamedImportAmd_0", "es6ImportNamedImportAmd_0", "es6ImportNamedImportAmd_0", "es6ImportNamedImportAmd_0", "es6ImportNamedImportAmd_0", "es6ImportNamedImportAmd_0"], function (require, exports, es6ImportNamedImportAmd_0_1, es6ImportNamedImportAmd_0_2, es6ImportNamedImportAmd_0_3, es6ImportNamedImportAmd_0_4, es6ImportNamedImportAmd_0_5, es6ImportNamedImportAmd_0_6, es6ImportNamedImportAmd_0_7, es6ImportNamedImportAmd_0_8, es6ImportNamedImportAmd_0_9) {
+    var xxxx = es6ImportNamedImportAmd_0_1.a;
+    var xxxx = es6ImportNamedImportAmd_0_2.a;
+    var xxxx = es6ImportNamedImportAmd_0_3.x;
+    var xxxx = es6ImportNamedImportAmd_0_3.a;
+    var xxxx = es6ImportNamedImportAmd_0_4.x;
+    var xxxx = es6ImportNamedImportAmd_0_5.m;
+    var xxxx = es6ImportNamedImportAmd_0_6.a1;
+    var xxxx = es6ImportNamedImportAmd_0_6.x1;
+    var xxxx = es6ImportNamedImportAmd_0_7.a1;
+    var xxxx = es6ImportNamedImportAmd_0_7.x1;
+    var z111 = es6ImportNamedImportAmd_0_8.z1;
+    var z2 = es6ImportNamedImportAmd_0_9.z2; // z2 shouldn't give redeclare error
 });
 
 
diff --git a/tests/baselines/reference/es6ImportNamedImportDts.js b/tests/baselines/reference/es6ImportNamedImportDts.js
index 877ae6fab74f3..a72632a737e7a 100644
--- a/tests/baselines/reference/es6ImportNamedImportDts.js
+++ b/tests/baselines/reference/es6ImportNamedImportDts.js
@@ -132,27 +132,27 @@ var aaaa1 = (function () {
 })();
 exports.aaaa1 = aaaa1;
 //// [client.js]
-var _server_1 = require("server");
-exports.xxxx = new _server_1.a();
-var _server_2 = require("server");
-exports.xxxx1 = new _server_2.a11();
-var _server_3 = require("server");
-exports.xxxx2 = new _server_3.x();
-exports.xxxx3 = new _server_3.a12();
-var _server_4 = require("server");
-exports.xxxx4 = new _server_4.x11();
-var _server_5 = require("server");
-exports.xxxx5 = new _server_5.m();
-var _server_6 = require("server");
-exports.xxxx6 = new _server_6.a1();
-exports.xxxx7 = new _server_6.x1();
-var _server_7 = require("server");
-exports.xxxx8 = new _server_7.a111();
-exports.xxxx9 = new _server_7.x111();
-var _server_8 = require("server");
-exports.z111 = new _server_8.z1();
-var _server_9 = require("server");
-exports.z2 = new _server_9.z2(); // z2 shouldn't give redeclare error
+var server_1 = require("server");
+exports.xxxx = new server_1.a();
+var server_2 = require("server");
+exports.xxxx1 = new server_2.a11();
+var server_3 = require("server");
+exports.xxxx2 = new server_3.x();
+exports.xxxx3 = new server_3.a12();
+var server_4 = require("server");
+exports.xxxx4 = new server_4.x11();
+var server_5 = require("server");
+exports.xxxx5 = new server_5.m();
+var server_6 = require("server");
+exports.xxxx6 = new server_6.a1();
+exports.xxxx7 = new server_6.x1();
+var server_7 = require("server");
+exports.xxxx8 = new server_7.a111();
+exports.xxxx9 = new server_7.x111();
+var server_8 = require("server");
+exports.z111 = new server_8.z1();
+var server_9 = require("server");
+exports.z2 = new server_9.z2(); // z2 shouldn't give redeclare error
 
 
 //// [server.d.ts]
diff --git a/tests/baselines/reference/es6ImportNamedImportInEs5.js b/tests/baselines/reference/es6ImportNamedImportInEs5.js
index fcb88d55b333a..9992508c00be5 100644
--- a/tests/baselines/reference/es6ImportNamedImportInEs5.js
+++ b/tests/baselines/reference/es6ImportNamedImportInEs5.js
@@ -51,27 +51,27 @@ exports.z1 = 10;
 exports.z2 = 10;
 exports.aaaa = 10;
 //// [es6ImportNamedImportInEs5_1.js]
-var _es6ImportNamedImportInEs5_0_1 = require("es6ImportNamedImportInEs5_0");
-var xxxx = _es6ImportNamedImportInEs5_0_1.a;
-var _es6ImportNamedImportInEs5_0_2 = require("es6ImportNamedImportInEs5_0");
-var xxxx = _es6ImportNamedImportInEs5_0_2.a;
-var _es6ImportNamedImportInEs5_0_3 = require("es6ImportNamedImportInEs5_0");
-var xxxx = _es6ImportNamedImportInEs5_0_3.x;
-var xxxx = _es6ImportNamedImportInEs5_0_3.a;
-var _es6ImportNamedImportInEs5_0_4 = require("es6ImportNamedImportInEs5_0");
-var xxxx = _es6ImportNamedImportInEs5_0_4.x;
-var _es6ImportNamedImportInEs5_0_5 = require("es6ImportNamedImportInEs5_0");
-var xxxx = _es6ImportNamedImportInEs5_0_5.m;
-var _es6ImportNamedImportInEs5_0_6 = require("es6ImportNamedImportInEs5_0");
-var xxxx = _es6ImportNamedImportInEs5_0_6.a1;
-var xxxx = _es6ImportNamedImportInEs5_0_6.x1;
-var _es6ImportNamedImportInEs5_0_7 = require("es6ImportNamedImportInEs5_0");
-var xxxx = _es6ImportNamedImportInEs5_0_7.a1;
-var xxxx = _es6ImportNamedImportInEs5_0_7.x1;
-var _es6ImportNamedImportInEs5_0_8 = require("es6ImportNamedImportInEs5_0");
-var z111 = _es6ImportNamedImportInEs5_0_8.z1;
-var _es6ImportNamedImportInEs5_0_9 = require("es6ImportNamedImportInEs5_0");
-var z2 = _es6ImportNamedImportInEs5_0_9.z2; // z2 shouldn't give redeclare error
+var es6ImportNamedImportInEs5_0_1 = require("es6ImportNamedImportInEs5_0");
+var xxxx = es6ImportNamedImportInEs5_0_1.a;
+var es6ImportNamedImportInEs5_0_2 = require("es6ImportNamedImportInEs5_0");
+var xxxx = es6ImportNamedImportInEs5_0_2.a;
+var es6ImportNamedImportInEs5_0_3 = require("es6ImportNamedImportInEs5_0");
+var xxxx = es6ImportNamedImportInEs5_0_3.x;
+var xxxx = es6ImportNamedImportInEs5_0_3.a;
+var es6ImportNamedImportInEs5_0_4 = require("es6ImportNamedImportInEs5_0");
+var xxxx = es6ImportNamedImportInEs5_0_4.x;
+var es6ImportNamedImportInEs5_0_5 = require("es6ImportNamedImportInEs5_0");
+var xxxx = es6ImportNamedImportInEs5_0_5.m;
+var es6ImportNamedImportInEs5_0_6 = require("es6ImportNamedImportInEs5_0");
+var xxxx = es6ImportNamedImportInEs5_0_6.a1;
+var xxxx = es6ImportNamedImportInEs5_0_6.x1;
+var es6ImportNamedImportInEs5_0_7 = require("es6ImportNamedImportInEs5_0");
+var xxxx = es6ImportNamedImportInEs5_0_7.a1;
+var xxxx = es6ImportNamedImportInEs5_0_7.x1;
+var es6ImportNamedImportInEs5_0_8 = require("es6ImportNamedImportInEs5_0");
+var z111 = es6ImportNamedImportInEs5_0_8.z1;
+var es6ImportNamedImportInEs5_0_9 = require("es6ImportNamedImportInEs5_0");
+var z2 = es6ImportNamedImportInEs5_0_9.z2; // z2 shouldn't give redeclare error
 
 
 //// [es6ImportNamedImportInEs5_0.d.ts]
diff --git a/tests/baselines/reference/es6ImportNamedImportInIndirectExportAssignment.js b/tests/baselines/reference/es6ImportNamedImportInIndirectExportAssignment.js
index 9c383ab3e3b36..f457e31f53c82 100644
--- a/tests/baselines/reference/es6ImportNamedImportInIndirectExportAssignment.js
+++ b/tests/baselines/reference/es6ImportNamedImportInIndirectExportAssignment.js
@@ -23,8 +23,8 @@ var a;
     a.c = c;
 })(a = exports.a || (exports.a = {}));
 //// [es6ImportNamedImportInIndirectExportAssignment_1.js]
-var _es6ImportNamedImportInIndirectExportAssignment_0 = require("es6ImportNamedImportInIndirectExportAssignment_0");
-var x = _es6ImportNamedImportInIndirectExportAssignment_0.a;
+var es6ImportNamedImportInIndirectExportAssignment_0_1 = require("es6ImportNamedImportInIndirectExportAssignment_0");
+var x = es6ImportNamedImportInIndirectExportAssignment_0_1.a;
 module.exports = x;
 
 
diff --git a/tests/baselines/reference/es6ImportNamedImportWithExport.js b/tests/baselines/reference/es6ImportNamedImportWithExport.js
index 71f4af721788c..60ba6bf706be4 100644
--- a/tests/baselines/reference/es6ImportNamedImportWithExport.js
+++ b/tests/baselines/reference/es6ImportNamedImportWithExport.js
@@ -50,27 +50,27 @@ exports.z1 = 10;
 exports.z2 = 10;
 exports.aaaa = 10;
 //// [client.js]
-var _server_1 = require("server");
-exports.xxxx = _server_1.a;
-var _server_2 = require("server");
-exports.xxxx = _server_2.a;
-var _server_3 = require("server");
-exports.xxxx = _server_3.x;
-exports.xxxx = _server_3.a;
-var _server_4 = require("server");
-exports.xxxx = _server_4.x;
-var _server_5 = require("server");
-exports.xxxx = _server_5.m;
-var _server_6 = require("server");
-exports.xxxx = _server_6.a1;
-exports.xxxx = _server_6.x1;
-var _server_7 = require("server");
-exports.xxxx = _server_7.a1;
-exports.xxxx = _server_7.x1;
-var _server_8 = require("server");
-exports.z111 = _server_8.z1;
-var _server_9 = require("server");
-exports.z2 = _server_9.z2; // z2 shouldn't give redeclare error
+var server_1 = require("server");
+exports.xxxx = server_1.a;
+var server_2 = require("server");
+exports.xxxx = server_2.a;
+var server_3 = require("server");
+exports.xxxx = server_3.x;
+exports.xxxx = server_3.a;
+var server_4 = require("server");
+exports.xxxx = server_4.x;
+var server_5 = require("server");
+exports.xxxx = server_5.m;
+var server_6 = require("server");
+exports.xxxx = server_6.a1;
+exports.xxxx = server_6.x1;
+var server_7 = require("server");
+exports.xxxx = server_7.a1;
+exports.xxxx = server_7.x1;
+var server_8 = require("server");
+exports.z111 = server_8.z1;
+var server_9 = require("server");
+exports.z2 = server_9.z2; // z2 shouldn't give redeclare error
 
 
 //// [server.d.ts]
diff --git a/tests/baselines/reference/es6ImportNamedImportWithTypesAndValues.js b/tests/baselines/reference/es6ImportNamedImportWithTypesAndValues.js
index 7852d2991bc8a..dcf99c5359a81 100644
--- a/tests/baselines/reference/es6ImportNamedImportWithTypesAndValues.js
+++ b/tests/baselines/reference/es6ImportNamedImportWithTypesAndValues.js
@@ -36,8 +36,8 @@ var C2 = (function () {
 })();
 exports.C2 = C2;
 //// [client.js]
-var _server = require("server"); // Shouldnt emit I and C2 into the js file and emit C and I in .d.ts file
-exports.cVal = new _server.C();
+var server_1 = require("server"); // Shouldnt emit I and C2 into the js file and emit C and I in .d.ts file
+exports.cVal = new server_1.C();
 
 
 //// [server.d.ts]
diff --git a/tests/baselines/reference/exportDefaultTypeAnnoation3.js b/tests/baselines/reference/exportDefaultTypeAnnoation3.js
index 069c8385e77e6..b29e7d2d9bc06 100644
--- a/tests/baselines/reference/exportDefaultTypeAnnoation3.js
+++ b/tests/baselines/reference/exportDefaultTypeAnnoation3.js
@@ -18,5 +18,5 @@ var s: string = d; // Error
 var d = require("mod");
 var s = d; // Error
 //// [reference2.js]
-var _mod = require("mod");
-var s = _mod.default; // Error
+var mod_1 = require("mod");
+var s = mod_1.default; // Error
diff --git a/tests/baselines/reference/giant.js b/tests/baselines/reference/giant.js
index 9de46f76b1bb8..cc532ff43d955 100644
--- a/tests/baselines/reference/giant.js
+++ b/tests/baselines/reference/giant.js
@@ -754,7 +754,7 @@ define(["require", "exports"], function (require, exports) {
         return C;
     })();
     var M;
-    (function (_M) {
+    (function (M_1) {
         var V;
         function F() {
         }
@@ -844,10 +844,10 @@ define(["require", "exports"], function (require, exports) {
             ;
             ;
         })(M || (M = {}));
-        _M.eV;
+        M_1.eV;
         function eF() {
         }
-        _M.eF = eF;
+        M_1.eF = eF;
         ;
         var eC = (function () {
             function eC() {
@@ -902,7 +902,7 @@ define(["require", "exports"], function (require, exports) {
             });
             return eC;
         })();
-        _M.eC = eC;
+        M_1.eC = eC;
         var eM;
         (function (eM) {
             var V;
@@ -934,7 +934,7 @@ define(["require", "exports"], function (require, exports) {
             ;
             ;
             ;
-        })(eM = _M.eM || (_M.eM = {}));
+        })(eM = M_1.eM || (M_1.eM = {}));
         ;
     })(M || (M = {}));
     exports.eV;
@@ -997,7 +997,7 @@ define(["require", "exports"], function (require, exports) {
     })();
     exports.eC = eC;
     var eM;
-    (function (_eM) {
+    (function (eM_1) {
         var V;
         function F() {
         }
@@ -1087,10 +1087,10 @@ define(["require", "exports"], function (require, exports) {
             ;
             ;
         })(M || (M = {}));
-        _eM.eV;
+        eM_1.eV;
         function eF() {
         }
-        _eM.eF = eF;
+        eM_1.eF = eF;
         ;
         var eC = (function () {
             function eC() {
@@ -1145,7 +1145,7 @@ define(["require", "exports"], function (require, exports) {
             });
             return eC;
         })();
-        _eM.eC = eC;
+        eM_1.eC = eC;
         var eM;
         (function (eM) {
             var V;
@@ -1177,7 +1177,7 @@ define(["require", "exports"], function (require, exports) {
             ;
             ;
             ;
-        })(eM = _eM.eM || (_eM.eM = {}));
+        })(eM = eM_1.eM || (eM_1.eM = {}));
         ;
     })(eM = exports.eM || (exports.eM = {}));
     ;
diff --git a/tests/baselines/reference/importAndVariableDeclarationConflict1.js b/tests/baselines/reference/importAndVariableDeclarationConflict1.js
index 78484b2c295a1..b812deec0ef45 100644
--- a/tests/baselines/reference/importAndVariableDeclarationConflict1.js
+++ b/tests/baselines/reference/importAndVariableDeclarationConflict1.js
@@ -9,8 +9,8 @@ var x = '';
 
 //// [importAndVariableDeclarationConflict1.js]
 var m;
-(function (_m) {
-    _m.m = '';
+(function (m_1) {
+    m_1.m = '';
 })(m || (m = {}));
 var x = m.m;
 var x = '';
diff --git a/tests/baselines/reference/importAndVariableDeclarationConflict2.js b/tests/baselines/reference/importAndVariableDeclarationConflict2.js
index bea146fe9bf0e..6d188b373b74a 100644
--- a/tests/baselines/reference/importAndVariableDeclarationConflict2.js
+++ b/tests/baselines/reference/importAndVariableDeclarationConflict2.js
@@ -13,8 +13,8 @@ class C {
 
 //// [importAndVariableDeclarationConflict2.js]
 var m;
-(function (_m) {
-    _m.m = '';
+(function (m_1) {
+    m_1.m = '';
 })(m || (m = {}));
 var x = m.m;
 var C = (function () {
diff --git a/tests/baselines/reference/importAndVariableDeclarationConflict3.js b/tests/baselines/reference/importAndVariableDeclarationConflict3.js
index 426d44bab2173..887aec16c59b0 100644
--- a/tests/baselines/reference/importAndVariableDeclarationConflict3.js
+++ b/tests/baselines/reference/importAndVariableDeclarationConflict3.js
@@ -9,8 +9,8 @@ import x = m.m;
 
 //// [importAndVariableDeclarationConflict3.js]
 var m;
-(function (_m) {
-    _m.m = '';
+(function (m_1) {
+    m_1.m = '';
 })(m || (m = {}));
 var x = m.m;
 var x = m.m;
diff --git a/tests/baselines/reference/importAndVariableDeclarationConflict4.js b/tests/baselines/reference/importAndVariableDeclarationConflict4.js
index 2adb78594a23a..4949df6366a42 100644
--- a/tests/baselines/reference/importAndVariableDeclarationConflict4.js
+++ b/tests/baselines/reference/importAndVariableDeclarationConflict4.js
@@ -9,8 +9,8 @@ import x = m.m;
 
 //// [importAndVariableDeclarationConflict4.js]
 var m;
-(function (_m) {
-    _m.m = '';
+(function (m_1) {
+    m_1.m = '';
 })(m || (m = {}));
 var x = '';
 var x = m.m;
diff --git a/tests/baselines/reference/importedModuleAddToGlobal.js b/tests/baselines/reference/importedModuleAddToGlobal.js
index 6685bec69e374..a848ccb504bde 100644
--- a/tests/baselines/reference/importedModuleAddToGlobal.js
+++ b/tests/baselines/reference/importedModuleAddToGlobal.js
@@ -18,13 +18,13 @@ module C {
 
 //// [importedModuleAddToGlobal.js]
 var B;
-(function (_B) {
+(function (B_1) {
     var B = (function () {
         function B() {
         }
         return B;
     })();
-    _B.B = B;
+    B_1.B = B;
 })(B || (B = {}));
 var C;
 (function (C) {
diff --git a/tests/baselines/reference/initializePropertiesWithRenamedLet.js b/tests/baselines/reference/initializePropertiesWithRenamedLet.js
index 902a23f5886e0..1d34d7c13fc86 100644
--- a/tests/baselines/reference/initializePropertiesWithRenamedLet.js
+++ b/tests/baselines/reference/initializePropertiesWithRenamedLet.js
@@ -19,28 +19,28 @@ if (true) {
 //// [initializePropertiesWithRenamedLet.js]
 var x0;
 if (true) {
-    var _x0;
+    var x0_1;
     var obj1 = {
-        x0: _x0
+        x0: x0_1
     };
     var obj2 = {
-        x0: _x0
+        x0: x0_1
     };
 }
 var x, y, z;
 if (true) {
-    var _x = ({
+    var x_1 = ({
         x: 0
     }).x;
-    var _y = ({
+    var y_1 = ({
         y: 0
     }).y;
-    var _z;
+    var z_1;
     (_a = {
         z: 0
-    }, _z = _a.z, _a);
+    }, z_1 = _a.z, _a);
     (_b = {
         z: 0
-    }, _z = _b.z, _b);
+    }, z_1 = _b.z, _b);
 }
 var _a, _b;
diff --git a/tests/baselines/reference/isDeclarationVisibleNodeKinds.js b/tests/baselines/reference/isDeclarationVisibleNodeKinds.js
index d357922f5bce6..8604ec493a2ab 100644
--- a/tests/baselines/reference/isDeclarationVisibleNodeKinds.js
+++ b/tests/baselines/reference/isDeclarationVisibleNodeKinds.js
@@ -72,67 +72,67 @@ module schema {
 //// [isDeclarationVisibleNodeKinds.js]
 // Function types
 var schema;
-(function (_schema) {
+(function (schema_1) {
     function createValidator1(schema) {
         return undefined;
     }
-    _schema.createValidator1 = createValidator1;
+    schema_1.createValidator1 = createValidator1;
 })(schema || (schema = {}));
 // Constructor types
 var schema;
-(function (_schema_1) {
+(function (schema_2) {
     function createValidator2(schema) {
         return undefined;
     }
-    _schema_1.createValidator2 = createValidator2;
+    schema_2.createValidator2 = createValidator2;
 })(schema || (schema = {}));
 // union types
 var schema;
-(function (_schema_2) {
+(function (schema_3) {
     function createValidator3(schema) {
         return undefined;
     }
-    _schema_2.createValidator3 = createValidator3;
+    schema_3.createValidator3 = createValidator3;
 })(schema || (schema = {}));
 // Array types
 var schema;
-(function (_schema_3) {
+(function (schema_4) {
     function createValidator4(schema) {
         return undefined;
     }
-    _schema_3.createValidator4 = createValidator4;
+    schema_4.createValidator4 = createValidator4;
 })(schema || (schema = {}));
 // TypeLiterals
 var schema;
-(function (_schema_4) {
+(function (schema_5) {
     function createValidator5(schema) {
         return undefined;
     }
-    _schema_4.createValidator5 = createValidator5;
+    schema_5.createValidator5 = createValidator5;
 })(schema || (schema = {}));
 // Tuple types
 var schema;
-(function (_schema_5) {
+(function (schema_6) {
     function createValidator6(schema) {
         return undefined;
     }
-    _schema_5.createValidator6 = createValidator6;
+    schema_6.createValidator6 = createValidator6;
 })(schema || (schema = {}));
 // Paren Types
 var schema;
-(function (_schema_6) {
+(function (schema_7) {
     function createValidator7(schema) {
         return undefined;
     }
-    _schema_6.createValidator7 = createValidator7;
+    schema_7.createValidator7 = createValidator7;
 })(schema || (schema = {}));
 // Type reference
 var schema;
-(function (_schema_7) {
+(function (schema_8) {
     function createValidator8(schema) {
         return undefined;
     }
-    _schema_7.createValidator8 = createValidator8;
+    schema_8.createValidator8 = createValidator8;
 })(schema || (schema = {}));
 var schema;
 (function (schema) {
diff --git a/tests/baselines/reference/letConstInCaseClauses.js b/tests/baselines/reference/letConstInCaseClauses.js
index 94840a11a2c74..33650dcaf4caf 100644
--- a/tests/baselines/reference/letConstInCaseClauses.js
+++ b/tests/baselines/reference/letConstInCaseClauses.js
@@ -34,28 +34,28 @@ var y = 20;
 var x = 10;
 var y = 20;
 {
-    var _x = 1;
-    var _y = 2;
-    console.log(_x);
-    switch (_x) {
+    var x_1 = 1;
+    var y_1 = 2;
+    console.log(x_1);
+    switch (x_1) {
         case 10:
-            var _x_1 = 20;
+            var x_2 = 20;
     }
-    switch (_y) {
+    switch (y_1) {
         case 10:
-            var _y_1 = 20;
+            var y_2 = 20;
     }
 }
 {
-    var _x_2 = 1;
-    var _y_2 = 2;
-    console.log(_x_2);
-    switch (_x_2) {
+    var x_3 = 1;
+    var y_3 = 2;
+    console.log(x_3);
+    switch (x_3) {
         case 10:
-            var _x_3 = 20;
+            var x_4 = 20;
     }
-    switch (_y_2) {
+    switch (y_3) {
         case 10:
-            var _y_3 = 20;
+            var y_4 = 20;
     }
 }
diff --git a/tests/baselines/reference/letConstMatchingParameterNames.js b/tests/baselines/reference/letConstMatchingParameterNames.js
index a11405b9f83c7..392f0e7ae943e 100644
--- a/tests/baselines/reference/letConstMatchingParameterNames.js
+++ b/tests/baselines/reference/letConstMatchingParameterNames.js
@@ -19,8 +19,8 @@ function a() {
 var parent = true;
 var parent2 = true;
 function a() {
-    var _parent = 1;
-    var _parent2 = 2;
+    var parent = 1;
+    var parent2 = 2;
     function b(parent, parent2) {
         use(parent);
         use(parent2);
diff --git a/tests/baselines/reference/letDeclarations-es5.js b/tests/baselines/reference/letDeclarations-es5.js
index 5246e91edfb76..1d4eb4afcbfef 100644
--- a/tests/baselines/reference/letDeclarations-es5.js
+++ b/tests/baselines/reference/letDeclarations-es5.js
@@ -20,7 +20,7 @@ var l3, l4, l5, l6;
 var l7 = false;
 var l8 = 23;
 var l9 = 0, l10 = "", l11 = null;
-for (var _l11 in {}) {
+for (var l11_1 in {}) {
 }
 for (var l12 = 0; l12 < 9; l12++) {
 }
diff --git a/tests/baselines/reference/letKeepNamesOfTopLevelItems.js b/tests/baselines/reference/letKeepNamesOfTopLevelItems.js
new file mode 100644
index 0000000000000..96fd31ae536dd
--- /dev/null
+++ b/tests/baselines/reference/letKeepNamesOfTopLevelItems.js
@@ -0,0 +1,19 @@
+//// [letKeepNamesOfTopLevelItems.ts]
+let x;
+function foo() {
+    let x;
+}
+
+module A {
+    let x;
+}
+
+//// [letKeepNamesOfTopLevelItems.js]
+var x;
+function foo() {
+    var x;
+}
+var A;
+(function (A) {
+    var x;
+})(A || (A = {}));
diff --git a/tests/baselines/reference/letKeepNamesOfTopLevelItems.types b/tests/baselines/reference/letKeepNamesOfTopLevelItems.types
new file mode 100644
index 0000000000000..952be1512a984
--- /dev/null
+++ b/tests/baselines/reference/letKeepNamesOfTopLevelItems.types
@@ -0,0 +1,17 @@
+=== tests/cases/compiler/letKeepNamesOfTopLevelItems.ts ===
+let x;
+>x : any
+
+function foo() {
+>foo : () => void
+
+    let x;
+>x : any
+}
+
+module A {
+>A : typeof A
+
+    let x;
+>x : any
+}
diff --git a/tests/baselines/reference/letShadowedByNameInNestedScope.errors.txt b/tests/baselines/reference/letShadowedByNameInNestedScope.errors.txt
new file mode 100644
index 0000000000000..b47e194f93eb1
--- /dev/null
+++ b/tests/baselines/reference/letShadowedByNameInNestedScope.errors.txt
@@ -0,0 +1,14 @@
+tests/cases/compiler/letShadowedByNameInNestedScope.ts(6,9): error TS2304: Cannot find name 'console'.
+
+
+==== tests/cases/compiler/letShadowedByNameInNestedScope.ts (1 errors) ====
+    var x;
+    function foo() {
+        let x = 0;
+        (function () {
+            var _x = 1;
+            console.log(x);
+            ~~~~~~~
+!!! error TS2304: Cannot find name 'console'.
+        })();
+    }
\ No newline at end of file
diff --git a/tests/baselines/reference/letShadowedByNameInNestedScope.js b/tests/baselines/reference/letShadowedByNameInNestedScope.js
new file mode 100644
index 0000000000000..648fe0b8e94df
--- /dev/null
+++ b/tests/baselines/reference/letShadowedByNameInNestedScope.js
@@ -0,0 +1,19 @@
+//// [letShadowedByNameInNestedScope.ts]
+var x;
+function foo() {
+    let x = 0;
+    (function () {
+        var _x = 1;
+        console.log(x);
+    })();
+}
+
+//// [letShadowedByNameInNestedScope.js]
+var x;
+function foo() {
+    var x = 0;
+    (function () {
+        var _x = 1;
+        console.log(x);
+    })();
+}
diff --git a/tests/baselines/reference/mergedModuleDeclarationCodeGen.js b/tests/baselines/reference/mergedModuleDeclarationCodeGen.js
index 88b949dd92023..d5cda7c91099d 100644
--- a/tests/baselines/reference/mergedModuleDeclarationCodeGen.js
+++ b/tests/baselines/reference/mergedModuleDeclarationCodeGen.js
@@ -19,10 +19,10 @@ export module X {
 var X;
 (function (X) {
     var Y;
-    (function (_Y) {
+    (function (Y_1) {
         var A = (function () {
             function A(Y) {
-                new _Y.B();
+                new Y_1.B();
             }
             return A;
         })();
diff --git a/tests/baselines/reference/mergedModuleDeclarationCodeGen2.js b/tests/baselines/reference/mergedModuleDeclarationCodeGen2.js
index 457bd12b8f082..06a590194f5f5 100644
--- a/tests/baselines/reference/mergedModuleDeclarationCodeGen2.js
+++ b/tests/baselines/reference/mergedModuleDeclarationCodeGen2.js
@@ -22,11 +22,11 @@ var my;
     })(data = my.data || (my.data = {}));
 })(my || (my = {}));
 var my;
-(function (_my) {
+(function (my_1) {
     var data;
-    (function (_data) {
+    (function (data_1) {
         function data(my) {
-            _data.foo.buz();
+            data_1.foo.buz();
         }
-    })(data = _my.data || (_my.data = {}));
+    })(data = my_1.data || (my_1.data = {}));
 })(my || (my = {}));
diff --git a/tests/baselines/reference/mergedModuleDeclarationCodeGen3.js b/tests/baselines/reference/mergedModuleDeclarationCodeGen3.js
index 0618346dd75ea..43c55ed8291af 100644
--- a/tests/baselines/reference/mergedModuleDeclarationCodeGen3.js
+++ b/tests/baselines/reference/mergedModuleDeclarationCodeGen3.js
@@ -19,14 +19,14 @@ var my;
     })(data = my.data || (my.data = {}));
 })(my || (my = {}));
 var my;
-(function (_my) {
+(function (my_1) {
     var data;
-    (function (_data) {
+    (function (data_1) {
         var foo;
-        (function (_foo) {
+        (function (foo_1) {
             function data(my, foo) {
-                _data.buz();
+                data_1.buz();
             }
-        })(foo = _data.foo || (_data.foo = {}));
-    })(data = _my.data || (_my.data = {}));
+        })(foo = data_1.foo || (data_1.foo = {}));
+    })(data = my_1.data || (my_1.data = {}));
 })(my || (my = {}));
diff --git a/tests/baselines/reference/mergedModuleDeclarationCodeGen4.js b/tests/baselines/reference/mergedModuleDeclarationCodeGen4.js
index 2463c9cae906a..af7f5bacef73b 100644
--- a/tests/baselines/reference/mergedModuleDeclarationCodeGen4.js
+++ b/tests/baselines/reference/mergedModuleDeclarationCodeGen4.js
@@ -20,7 +20,7 @@ module superContain {
 var superContain;
 (function (superContain) {
     var contain;
-    (function (_contain) {
+    (function (contain_1) {
         var my;
         (function (my) {
             var buz;
@@ -32,19 +32,19 @@ var superContain;
                     data.foo = foo;
                 })(data = buz.data || (buz.data = {}));
             })(buz = my.buz || (my.buz = {}));
-        })(my = _contain.my || (_contain.my = {}));
+        })(my = contain_1.my || (contain_1.my = {}));
         var my;
-        (function (_my) {
+        (function (my_1) {
             var buz;
-            (function (_buz) {
+            (function (buz_1) {
                 var data;
-                (function (_data) {
+                (function (data_1) {
                     function bar(contain, my, buz, data) {
-                        _data.foo();
+                        data_1.foo();
                     }
-                    _data.bar = bar;
-                })(data = _buz.data || (_buz.data = {}));
-            })(buz = _my.buz || (_my.buz = {}));
-        })(my = _contain.my || (_contain.my = {}));
+                    data_1.bar = bar;
+                })(data = buz_1.data || (buz_1.data = {}));
+            })(buz = my_1.buz || (my_1.buz = {}));
+        })(my = contain_1.my || (contain_1.my = {}));
     })(contain = superContain.contain || (superContain.contain = {}));
 })(superContain || (superContain = {}));
diff --git a/tests/baselines/reference/mergedModuleDeclarationCodeGen5.js b/tests/baselines/reference/mergedModuleDeclarationCodeGen5.js
index 2c8e0bb79e4fb..4bbad2e567868 100644
--- a/tests/baselines/reference/mergedModuleDeclarationCodeGen5.js
+++ b/tests/baselines/reference/mergedModuleDeclarationCodeGen5.js
@@ -20,7 +20,7 @@ module M.buz.plop {
 
 //// [mergedModuleDeclarationCodeGen5.js]
 var M;
-(function (_M) {
+(function (M_1) {
     var buz;
     (function (buz) {
         var plop;
@@ -32,14 +32,14 @@ var M;
             }
             plop.M = M;
         })(plop = buz.plop || (buz.plop = {}));
-    })(buz = _M.buz || (_M.buz = {}));
+    })(buz = M_1.buz || (M_1.buz = {}));
 })(M || (M = {}));
 var M;
 (function (M) {
     var buz;
-    (function (_buz) {
+    (function (buz_1) {
         var plop;
-        (function (_plop) {
+        (function (plop_1) {
             function gunk() {
             }
             function buz() {
@@ -49,17 +49,17 @@ var M;
                 }
                 return fudge;
             })();
-            _plop.fudge = fudge;
+            plop_1.fudge = fudge;
             (function (plop) {
-            })(_plop.plop || (_plop.plop = {}));
-            var plop = _plop.plop;
+            })(plop_1.plop || (plop_1.plop = {}));
+            var plop = plop_1.plop;
             // Emit these references as follows
             var v1 = gunk; // gunk
             var v2 = buz; // buz
-            _plop.v3 = _plop.doom; // _plop.doom
-            _plop.v4 = _plop.M; // _plop.M
-            _plop.v5 = fudge; // fudge
-            _plop.v6 = plop; // plop
-        })(plop = _buz.plop || (_buz.plop = {}));
+            plop_1.v3 = plop_1.doom; // _plop.doom
+            plop_1.v4 = plop_1.M; // _plop.M
+            plop_1.v5 = fudge; // fudge
+            plop_1.v6 = plop; // plop
+        })(plop = buz_1.plop || (buz_1.plop = {}));
     })(buz = M.buz || (M.buz = {}));
 })(M || (M = {}));
diff --git a/tests/baselines/reference/moduleSharesNameWithImportDeclarationInsideIt.js b/tests/baselines/reference/moduleSharesNameWithImportDeclarationInsideIt.js
index 983dc004acf31..f9a90fd515155 100644
--- a/tests/baselines/reference/moduleSharesNameWithImportDeclarationInsideIt.js
+++ b/tests/baselines/reference/moduleSharesNameWithImportDeclarationInsideIt.js
@@ -25,11 +25,11 @@ var Z;
 var A;
 (function (A) {
     var M;
-    (function (_M) {
+    (function (M_1) {
         var M = Z.M;
         function bar() {
         }
-        _M.bar = bar;
+        M_1.bar = bar;
         M.bar(); // Should call Z.M.bar
     })(M = A.M || (A.M = {}));
 })(A || (A = {}));
diff --git a/tests/baselines/reference/moduleSharesNameWithImportDeclarationInsideIt3.js b/tests/baselines/reference/moduleSharesNameWithImportDeclarationInsideIt3.js
index c11b36f643a30..efdcebe84e96d 100644
--- a/tests/baselines/reference/moduleSharesNameWithImportDeclarationInsideIt3.js
+++ b/tests/baselines/reference/moduleSharesNameWithImportDeclarationInsideIt3.js
@@ -30,11 +30,11 @@ var Z;
 var A;
 (function (A) {
     var M;
-    (function (_M) {
+    (function (M_1) {
         var M = Z.M;
         function bar() {
         }
-        _M.bar = bar;
+        M_1.bar = bar;
         M.bar(); // Should call Z.M.bar
     })(M = A.M || (A.M = {}));
 })(A || (A = {}));
diff --git a/tests/baselines/reference/moduleSharesNameWithImportDeclarationInsideIt4.js b/tests/baselines/reference/moduleSharesNameWithImportDeclarationInsideIt4.js
index c61f3d4dd9d73..e9cd456f3f3f8 100644
--- a/tests/baselines/reference/moduleSharesNameWithImportDeclarationInsideIt4.js
+++ b/tests/baselines/reference/moduleSharesNameWithImportDeclarationInsideIt4.js
@@ -26,11 +26,11 @@ var Z;
 var A;
 (function (A) {
     var M;
-    (function (_M) {
+    (function (M_1) {
         var M = Z.M;
         function bar() {
         }
-        _M.bar = bar;
+        M_1.bar = bar;
         M.bar(); // Should call Z.M.bar
     })(M = A.M || (A.M = {}));
 })(A || (A = {}));
diff --git a/tests/baselines/reference/moduleSharesNameWithImportDeclarationInsideIt5.js b/tests/baselines/reference/moduleSharesNameWithImportDeclarationInsideIt5.js
index 0bc314ccc0706..72aa36022634d 100644
--- a/tests/baselines/reference/moduleSharesNameWithImportDeclarationInsideIt5.js
+++ b/tests/baselines/reference/moduleSharesNameWithImportDeclarationInsideIt5.js
@@ -30,10 +30,10 @@ var Z;
 var A;
 (function (A) {
     var M;
-    (function (_M) {
+    (function (M_1) {
         function bar() {
         }
-        _M.bar = bar;
+        M_1.bar = bar;
         M.bar(); // Should call Z.M.bar
     })(M = A.M || (A.M = {}));
 })(A || (A = {}));
diff --git a/tests/baselines/reference/moduleSharesNameWithImportDeclarationInsideIt6.js b/tests/baselines/reference/moduleSharesNameWithImportDeclarationInsideIt6.js
index 4ba0a33c29a0c..fbad13359b8eb 100644
--- a/tests/baselines/reference/moduleSharesNameWithImportDeclarationInsideIt6.js
+++ b/tests/baselines/reference/moduleSharesNameWithImportDeclarationInsideIt6.js
@@ -24,9 +24,9 @@ var Z;
 var A;
 (function (A) {
     var M;
-    (function (_M) {
+    (function (M_1) {
         function bar() {
         }
-        _M.bar = bar;
+        M_1.bar = bar;
     })(M = A.M || (A.M = {}));
 })(A || (A = {}));
diff --git a/tests/baselines/reference/moduleWithStatementsOfEveryKind.js b/tests/baselines/reference/moduleWithStatementsOfEveryKind.js
index 5161f72d5f023..cab0d35aa5a20 100644
--- a/tests/baselines/reference/moduleWithStatementsOfEveryKind.js
+++ b/tests/baselines/reference/moduleWithStatementsOfEveryKind.js
@@ -66,7 +66,7 @@ var __extends = this.__extends || function (d, b) {
     d.prototype = new __();
 };
 var A;
-(function (_A) {
+(function (A_1) {
     var A = (function () {
         function A() {
         }
diff --git a/tests/baselines/reference/nameCollision.js b/tests/baselines/reference/nameCollision.js
index fe7bb3a891975..0e559b7091cc8 100644
--- a/tests/baselines/reference/nameCollision.js
+++ b/tests/baselines/reference/nameCollision.js
@@ -48,7 +48,7 @@ module D {
 
 //// [nameCollision.js]
 var A;
-(function (_A_1) {
+(function (A_1) {
     // these 2 statements force an underscore before the 'A' 
     // in the generated function call.
     var A = 12;
@@ -59,7 +59,7 @@ var B;
     var A = 12;
 })(B || (B = {}));
 var B;
-(function (_B) {
+(function (B_1) {
     // re-opened module with colliding name
     // this should add an underscore.
     var B = (function () {
@@ -69,29 +69,29 @@ var B;
     })();
 })(B || (B = {}));
 var X;
-(function (_X) {
+(function (X_1) {
     var X = 13;
     var Y;
-    (function (_Y) {
+    (function (Y_1) {
         var Y = 13;
         var Z;
-        (function (_Z) {
+        (function (Z_1) {
             var X = 12;
             var Y = 12;
             var Z = 12;
-        })(Z = _Y.Z || (_Y.Z = {}));
-    })(Y = _X.Y || (_X.Y = {}));
+        })(Z = Y_1.Z || (Y_1.Z = {}));
+    })(Y = X_1.Y || (X_1.Y = {}));
 })(X || (X = {}));
 var Y;
-(function (_Y_1) {
+(function (Y_2) {
     var Y;
-    (function (_Y_2) {
+    (function (Y_3) {
         (function (Y) {
             Y[Y["Red"] = 0] = "Red";
             Y[Y["Blue"] = 1] = "Blue";
-        })(_Y_2.Y || (_Y_2.Y = {}));
-        var Y = _Y_2.Y;
-    })(Y = _Y_1.Y || (_Y_1.Y = {}));
+        })(Y_3.Y || (Y_3.Y = {}));
+        var Y = Y_3.Y;
+    })(Y = Y_2.Y || (Y_2.Y = {}));
 })(Y || (Y = {}));
 // no collision, since interface doesn't
 // generate code.
diff --git a/tests/baselines/reference/overloadResolutionOverNonCTLambdas.js b/tests/baselines/reference/overloadResolutionOverNonCTLambdas.js
index d0ced9921469c..86e84ced58f0f 100644
--- a/tests/baselines/reference/overloadResolutionOverNonCTLambdas.js
+++ b/tests/baselines/reference/overloadResolutionOverNonCTLambdas.js
@@ -39,8 +39,8 @@ var Bugs;
         }
         var result = message.replace(/\{(\d+)\}/g, function (match) {
             var rest = [];
-            for (var _a = 1; _a < arguments.length; _a++) {
-                rest[_a - 1] = arguments[_a];
+            for (var _i = 1; _i < arguments.length; _i++) {
+                rest[_i - 1] = arguments[_i];
             }
             var index = rest[0];
             return typeof args[index] !== 'undefined' ? args[index] : match;
diff --git a/tests/baselines/reference/privacyGloImportParseErrors.js b/tests/baselines/reference/privacyGloImportParseErrors.js
index 3b82d65a07bca..d5a089a7678f2 100644
--- a/tests/baselines/reference/privacyGloImportParseErrors.js
+++ b/tests/baselines/reference/privacyGloImportParseErrors.js
@@ -238,7 +238,7 @@ var glo_M1_public;
     glo_M1_public.v2;
 })(glo_M1_public || (glo_M1_public = {}));
 var m2;
-(function (_m2) {
+(function (m2_1) {
     var m4;
     (function (m4) {
         var a = 10;
diff --git a/tests/baselines/reference/privacyImportParseErrors.js b/tests/baselines/reference/privacyImportParseErrors.js
index 7a875fa12d11d..90e4a7cb097f4 100644
--- a/tests/baselines/reference/privacyImportParseErrors.js
+++ b/tests/baselines/reference/privacyImportParseErrors.js
@@ -566,14 +566,14 @@ var glo_im4_private_v4_private = glo_im4_private.f1();
 exports.glo_im1_public = glo_M1_public;
 exports.glo_im2_public = glo_M3_private;
 var m2;
-(function (_m2) {
+(function (m2_1) {
     var m4;
     (function (m4) {
         var a = 10;
     })(m4 || (m4 = {}));
 })(m2 || (m2 = {}));
 var m3;
-(function (_m3) {
+(function (m3_1) {
     var m4;
     (function (m4) {
         var a = 10;
diff --git a/tests/baselines/reference/recursiveClassReferenceTest.js b/tests/baselines/reference/recursiveClassReferenceTest.js
index f565f8f23d08a..5f8be8bfdf1dd 100644
--- a/tests/baselines/reference/recursiveClassReferenceTest.js
+++ b/tests/baselines/reference/recursiveClassReferenceTest.js
@@ -116,7 +116,7 @@ var Sample;
     var Actions;
     (function (Actions) {
         var Thing;
-        (function (_Thing_1) {
+        (function (Thing_1) {
             var Find;
             (function (Find) {
                 var StartFindAction = (function () {
@@ -131,7 +131,7 @@ var Sample;
                     return StartFindAction;
                 })();
                 Find.StartFindAction = StartFindAction;
-            })(Find = _Thing_1.Find || (_Thing_1.Find = {}));
+            })(Find = Thing_1.Find || (Thing_1.Find = {}));
         })(Thing = Actions.Thing || (Actions.Thing = {}));
     })(Actions = Sample.Actions || (Sample.Actions = {}));
 })(Sample || (Sample = {}));
diff --git a/tests/baselines/reference/recursiveClassReferenceTest.js.map b/tests/baselines/reference/recursiveClassReferenceTest.js.map
index d77875f10e4a4..acc518edacac8 100644
--- a/tests/baselines/reference/recursiveClassReferenceTest.js.map
+++ b/tests/baselines/reference/recursiveClassReferenceTest.js.map
@@ -1,2 +1,2 @@
 //// [recursiveClassReferenceTest.js.map]
-{"version":3,"file":"recursiveClassReferenceTest.js","sourceRoot":"","sources":["recursiveClassReferenceTest.ts"],"names":["Sample","Sample.Actions","Sample.Actions.Thing","Sample.Actions.Thing.Find","Sample.Actions.Thing.Find.StartFindAction","Sample.Actions.Thing.Find.StartFindAction.constructor","Sample.Actions.Thing.Find.StartFindAction.getId","Sample.Actions.Thing.Find.StartFindAction.run","Sample.Thing","Sample.Thing.Widgets","Sample.Thing.Widgets.FindWidget","Sample.Thing.Widgets.FindWidget.constructor","Sample.Thing.Widgets.FindWidget.gar","Sample.Thing.Widgets.FindWidget.getDomNode","Sample.Thing.Widgets.FindWidget.destroy","AbstractMode","AbstractMode.constructor","AbstractMode.getInitialState","Sample.Thing.Languages","Sample.Thing.Languages.PlainText","Sample.Thing.Languages.PlainText.State","Sample.Thing.Languages.PlainText.State.constructor","Sample.Thing.Languages.PlainText.State.clone","Sample.Thing.Languages.PlainText.State.equals","Sample.Thing.Languages.PlainText.State.getMode","Sample.Thing.Languages.PlainText.Mode","Sample.Thing.Languages.PlainText.Mode.constructor","Sample.Thing.Languages.PlainText.Mode.getInitialState"],"mappings":"AAAA,iEAAiE;AACjE,0EAA0E;;;;;;;AA8B1E,IAAO,MAAM,CAUZ;AAVD,WAAO,MAAM;IAACA,IAAAA,OAAOA,CAUpBA;IAVaA,WAAAA,OAAOA;QAACC,IAAAA,KAAKA,CAU1BA;QAVqBA,WAAAA,QAAKA;YAACC,IAAAA,IAAIA,CAU/BA;YAV2BA,WAAAA,IAAIA,EAACA,CAACA;gBACjCC;oBAAAC;oBAQAC,CAACA;oBANOD,+BAAKA,GAAZA;wBAAiBE,MAAMA,CAACA,IAAIA,CAACA;oBAACA,CAACA;oBAExBF,6BAAGA,GAAVA,UAAWA,KAA6BA;wBAEvCG,MAAMA,CAACA,IAAIA,CAACA;oBACbA,CAACA;oBACFH,sBAACA;gBAADA,CAACA,AARDD,IAQCA;gBARYA,oBAAeA,kBAQ3BA,CAAAA;YACFA,CAACA,EAV2BD,IAAIA,GAAJA,aAAIA,KAAJA,aAAIA,QAU/BA;QAADA,CAACA,EAVqBD,KAAKA,GAALA,aAAKA,KAALA,aAAKA,QAU1BA;IAADA,CAACA,EAVaD,OAAOA,GAAPA,cAAOA,KAAPA,cAAOA,QAUpBA;AAADA,CAACA,EAVM,MAAM,KAAN,MAAM,QAUZ;AAED,IAAO,MAAM,CAoBZ;AApBD,WAAO,MAAM;IAACA,IAAAA,KAAKA,CAoBlBA;IApBaA,WAAAA,KAAKA;QAACQ,IAAAA,OAAOA,CAoB1BA;QApBmBA,WAAAA,OAAOA,EAACA,CAACA;YAC5BC;gBAKCC,oBAAoBA,SAAkCA;oBAAlCC,cAASA,GAATA,SAASA,CAAyBA;oBAD9CA,YAAOA,GAAOA,IAAIA,CAACA;oBAGvBA,AADAA,aAAaA;oBACbA,SAASA,CAACA,SAASA,CAACA,WAAWA,EAAEA,IAAIA,CAACA,CAACA;gBAC3CA,CAACA;gBANMD,wBAAGA,GAAVA,UAAWA,MAAyCA;oBAAIE,EAAEA,CAACA,CAACA,IAAIA,CAACA,CAACA,CAACA;wBAAAA,MAAMA,CAACA,MAAMA,CAACA,IAAIA,CAACA,CAACA;oBAAAA,CAACA;gBAAAA,CAACA;gBAQlFF,+BAAUA,GAAjBA;oBACCG,MAAMA,CAACA,OAAOA,CAACA;gBAChBA,CAACA;gBAEMH,4BAAOA,GAAdA;gBAEAI,CAACA;gBAEFJ,iBAACA;YAADA,CAACA,AAlBDD,IAkBCA;YAlBYA,kBAAUA,aAkBtBA,CAAAA;QACFA,CAACA,EApBmBD,OAAOA,GAAPA,aAAOA,KAAPA,aAAOA,QAoB1BA;IAADA,CAACA,EApBaR,KAAKA,GAALA,YAAKA,KAALA,YAAKA,QAoBlBA;AAADA,CAACA,EApBM,MAAM,KAAN,MAAM,QAoBZ;AAGD;IAAAe;IAAuFC,CAACA;IAA3CD,sCAAeA,GAAtBA;QAAmCE,MAAMA,CAACA,IAAIA,CAACA;IAAAA,CAACA;IAACF,mBAACA;AAADA,CAACA,AAAxF,IAAwF;AASxF,IAAO,MAAM,CAwBZ;AAxBD,WAAO,MAAM;IAACf,IAAAA,KAAKA,CAwBlBA;IAxBaA,WAAAA,KAAKA;QAACQ,IAAAA,SAASA,CAwB5BA;QAxBmBA,WAAAA,SAASA;YAACU,IAAAA,SAASA,CAwBtCA;YAxB6BA,WAAAA,SAASA,EAACA,CAACA;gBAExCC;oBACOC,eAAoBA,IAAWA;wBAAXC,SAAIA,GAAJA,IAAIA,CAAOA;oBAAIA,CAACA;oBACnCD,qBAAKA,GAAZA;wBACCE,MAAMA,CAACA,IAAIA,CAACA;oBACbA,CAACA;oBAEMF,sBAAMA,GAAbA,UAAcA,KAAYA;wBACzBG,MAAMA,CAACA,IAAIA,KAAKA,KAAKA,CAACA;oBACvBA,CAACA;oBAEMH,uBAAOA,GAAdA;wBAA0BI,MAAMA,CAACA,IAAIA,CAACA;oBAACA,CAACA;oBACzCJ,YAACA;gBAADA,CAACA,AAXDD,IAWCA;gBAXYA,eAAKA,QAWjBA,CAAAA;gBAEDA;oBAA0BM,wBAAYA;oBAAtCA;wBAA0BC,8BAAYA;oBAQtCA,CAACA;oBANAD,aAAaA;oBACNA,8BAAeA,GAAtBA;wBACCE,MAAMA,CAACA,IAAIA,KAAKA,CAACA,IAAIA,CAACA,CAACA;oBACxBA,CAACA;oBAGFF,WAACA;gBAADA,CAACA,AARDN,EAA0BA,YAAYA,EAQrCA;gBARYA,cAAIA,OAQhBA,CAAAA;YACFA,CAACA,EAxB6BD,SAASA,GAATA,mBAASA,KAATA,mBAASA,QAwBtCA;QAADA,CAACA,EAxBmBV,SAASA,GAATA,eAASA,KAATA,eAASA,QAwB5BA;IAADA,CAACA,EAxBaR,KAAKA,GAALA,YAAKA,KAALA,YAAKA,QAwBlBA;AAADA,CAACA,EAxBM,MAAM,KAAN,MAAM,QAwBZ"}
\ No newline at end of file
+{"version":3,"file":"recursiveClassReferenceTest.js","sourceRoot":"","sources":["recursiveClassReferenceTest.ts"],"names":["Sample","Sample.Actions","Sample.Actions.Thing","Sample.Actions.Thing.Find","Sample.Actions.Thing.Find.StartFindAction","Sample.Actions.Thing.Find.StartFindAction.constructor","Sample.Actions.Thing.Find.StartFindAction.getId","Sample.Actions.Thing.Find.StartFindAction.run","Sample.Thing","Sample.Thing.Widgets","Sample.Thing.Widgets.FindWidget","Sample.Thing.Widgets.FindWidget.constructor","Sample.Thing.Widgets.FindWidget.gar","Sample.Thing.Widgets.FindWidget.getDomNode","Sample.Thing.Widgets.FindWidget.destroy","AbstractMode","AbstractMode.constructor","AbstractMode.getInitialState","Sample.Thing.Languages","Sample.Thing.Languages.PlainText","Sample.Thing.Languages.PlainText.State","Sample.Thing.Languages.PlainText.State.constructor","Sample.Thing.Languages.PlainText.State.clone","Sample.Thing.Languages.PlainText.State.equals","Sample.Thing.Languages.PlainText.State.getMode","Sample.Thing.Languages.PlainText.Mode","Sample.Thing.Languages.PlainText.Mode.constructor","Sample.Thing.Languages.PlainText.Mode.getInitialState"],"mappings":"AAAA,iEAAiE;AACjE,0EAA0E;;;;;;;AA8B1E,IAAO,MAAM,CAUZ;AAVD,WAAO,MAAM;IAACA,IAAAA,OAAOA,CAUpBA;IAVaA,WAAAA,OAAOA;QAACC,IAAAA,KAAKA,CAU1BA;QAVqBA,WAAAA,OAAKA;YAACC,IAAAA,IAAIA,CAU/BA;YAV2BA,WAAAA,IAAIA,EAACA,CAACA;gBACjCC;oBAAAC;oBAQAC,CAACA;oBANOD,+BAAKA,GAAZA;wBAAiBE,MAAMA,CAACA,IAAIA,CAACA;oBAACA,CAACA;oBAExBF,6BAAGA,GAAVA,UAAWA,KAA6BA;wBAEvCG,MAAMA,CAACA,IAAIA,CAACA;oBACbA,CAACA;oBACFH,sBAACA;gBAADA,CAACA,AARDD,IAQCA;gBARYA,oBAAeA,kBAQ3BA,CAAAA;YACFA,CAACA,EAV2BD,IAAIA,GAAJA,YAAIA,KAAJA,YAAIA,QAU/BA;QAADA,CAACA,EAVqBD,KAAKA,GAALA,aAAKA,KAALA,aAAKA,QAU1BA;IAADA,CAACA,EAVaD,OAAOA,GAAPA,cAAOA,KAAPA,cAAOA,QAUpBA;AAADA,CAACA,EAVM,MAAM,KAAN,MAAM,QAUZ;AAED,IAAO,MAAM,CAoBZ;AApBD,WAAO,MAAM;IAACA,IAAAA,KAAKA,CAoBlBA;IApBaA,WAAAA,KAAKA;QAACQ,IAAAA,OAAOA,CAoB1BA;QApBmBA,WAAAA,OAAOA,EAACA,CAACA;YAC5BC;gBAKCC,oBAAoBA,SAAkCA;oBAAlCC,cAASA,GAATA,SAASA,CAAyBA;oBAD9CA,YAAOA,GAAOA,IAAIA,CAACA;oBAGvBA,AADAA,aAAaA;oBACbA,SAASA,CAACA,SAASA,CAACA,WAAWA,EAAEA,IAAIA,CAACA,CAACA;gBAC3CA,CAACA;gBANMD,wBAAGA,GAAVA,UAAWA,MAAyCA;oBAAIE,EAAEA,CAACA,CAACA,IAAIA,CAACA,CAACA,CAACA;wBAAAA,MAAMA,CAACA,MAAMA,CAACA,IAAIA,CAACA,CAACA;oBAAAA,CAACA;gBAAAA,CAACA;gBAQlFF,+BAAUA,GAAjBA;oBACCG,MAAMA,CAACA,OAAOA,CAACA;gBAChBA,CAACA;gBAEMH,4BAAOA,GAAdA;gBAEAI,CAACA;gBAEFJ,iBAACA;YAADA,CAACA,AAlBDD,IAkBCA;YAlBYA,kBAAUA,aAkBtBA,CAAAA;QACFA,CAACA,EApBmBD,OAAOA,GAAPA,aAAOA,KAAPA,aAAOA,QAoB1BA;IAADA,CAACA,EApBaR,KAAKA,GAALA,YAAKA,KAALA,YAAKA,QAoBlBA;AAADA,CAACA,EApBM,MAAM,KAAN,MAAM,QAoBZ;AAGD;IAAAe;IAAuFC,CAACA;IAA3CD,sCAAeA,GAAtBA;QAAmCE,MAAMA,CAACA,IAAIA,CAACA;IAAAA,CAACA;IAACF,mBAACA;AAADA,CAACA,AAAxF,IAAwF;AASxF,IAAO,MAAM,CAwBZ;AAxBD,WAAO,MAAM;IAACf,IAAAA,KAAKA,CAwBlBA;IAxBaA,WAAAA,KAAKA;QAACQ,IAAAA,SAASA,CAwB5BA;QAxBmBA,WAAAA,SAASA;YAACU,IAAAA,SAASA,CAwBtCA;YAxB6BA,WAAAA,SAASA,EAACA,CAACA;gBAExCC;oBACOC,eAAoBA,IAAWA;wBAAXC,SAAIA,GAAJA,IAAIA,CAAOA;oBAAIA,CAACA;oBACnCD,qBAAKA,GAAZA;wBACCE,MAAMA,CAACA,IAAIA,CAACA;oBACbA,CAACA;oBAEMF,sBAAMA,GAAbA,UAAcA,KAAYA;wBACzBG,MAAMA,CAACA,IAAIA,KAAKA,KAAKA,CAACA;oBACvBA,CAACA;oBAEMH,uBAAOA,GAAdA;wBAA0BI,MAAMA,CAACA,IAAIA,CAACA;oBAACA,CAACA;oBACzCJ,YAACA;gBAADA,CAACA,AAXDD,IAWCA;gBAXYA,eAAKA,QAWjBA,CAAAA;gBAEDA;oBAA0BM,wBAAYA;oBAAtCA;wBAA0BC,8BAAYA;oBAQtCA,CAACA;oBANAD,aAAaA;oBACNA,8BAAeA,GAAtBA;wBACCE,MAAMA,CAACA,IAAIA,KAAKA,CAACA,IAAIA,CAACA,CAACA;oBACxBA,CAACA;oBAGFF,WAACA;gBAADA,CAACA,AARDN,EAA0BA,YAAYA,EAQrCA;gBARYA,cAAIA,OAQhBA,CAAAA;YACFA,CAACA,EAxB6BD,SAASA,GAATA,mBAASA,KAATA,mBAASA,QAwBtCA;QAADA,CAACA,EAxBmBV,SAASA,GAATA,eAASA,KAATA,eAASA,QAwB5BA;IAADA,CAACA,EAxBaR,KAAKA,GAALA,YAAKA,KAALA,YAAKA,QAwBlBA;AAADA,CAACA,EAxBM,MAAM,KAAN,MAAM,QAwBZ"}
\ No newline at end of file
diff --git a/tests/baselines/reference/recursiveClassReferenceTest.sourcemap.txt b/tests/baselines/reference/recursiveClassReferenceTest.sourcemap.txt
index 47bb3f2d18ab8..7e1295d630613 100644
--- a/tests/baselines/reference/recursiveClassReferenceTest.sourcemap.txt
+++ b/tests/baselines/reference/recursiveClassReferenceTest.sourcemap.txt
@@ -139,7 +139,7 @@ sourceFile:recursiveClassReferenceTest.ts
 2 >        ^^^^
 3 >            ^^^^^
 4 >                 ^
-5 >                  ^^^^^^^^^^^^^->
+5 >                  ^^^^^^^^^^^^->
 1 >.
 2 >        
 3 >            Thing
@@ -159,16 +159,16 @@ sourceFile:recursiveClassReferenceTest.ts
 3 >Emitted(13, 18) Source(32, 28) + SourceIndex(0) name (Sample.Actions)
 4 >Emitted(13, 19) Source(42, 2) + SourceIndex(0) name (Sample.Actions)
 ---
->>>        (function (_Thing_1) {
+>>>        (function (Thing_1) {
 1->^^^^^^^^
 2 >        ^^^^^^^^^^^
-3 >                   ^^^^^^^^
+3 >                   ^^^^^^^
 1->
 2 >        
 3 >                   Thing
 1->Emitted(14, 9) Source(32, 23) + SourceIndex(0) name (Sample.Actions)
 2 >Emitted(14, 20) Source(32, 23) + SourceIndex(0) name (Sample.Actions)
-3 >Emitted(14, 28) Source(32, 28) + SourceIndex(0) name (Sample.Actions)
+3 >Emitted(14, 27) Source(32, 28) + SourceIndex(0) name (Sample.Actions)
 ---
 >>>            var Find;
 1 >^^^^^^^^^^^^
@@ -365,7 +365,7 @@ sourceFile:recursiveClassReferenceTest.ts
 2 >                ^^^^^^^^^^^^^^^^^^^^
 3 >                                    ^^^^^^^^^^^^^^^^^^
 4 >                                                      ^
-5 >                                                       ^^^^^^^->
+5 >                                                       ^^^^^->
 1->
 2 >                StartFindAction
 3 >                                     implements Sample.Thing.IAction {
@@ -383,16 +383,16 @@ sourceFile:recursiveClassReferenceTest.ts
 3 >Emitted(28, 55) Source(41, 3) + SourceIndex(0) name (Sample.Actions.Thing.Find)
 4 >Emitted(28, 56) Source(41, 3) + SourceIndex(0) name (Sample.Actions.Thing.Find)
 ---
->>>            })(Find = _Thing_1.Find || (_Thing_1.Find = {}));
+>>>            })(Find = Thing_1.Find || (Thing_1.Find = {}));
 1->^^^^^^^^^^^^
 2 >            ^
 3 >             ^^
 4 >               ^^^^
 5 >                   ^^^
-6 >                      ^^^^^^^^^^^^^
-7 >                                   ^^^^^
-8 >                                        ^^^^^^^^^^^^^
-9 >                                                     ^^^^^^^^
+6 >                      ^^^^^^^^^^^^
+7 >                                  ^^^^^
+8 >                                       ^^^^^^^^^^^^
+9 >                                                   ^^^^^^^^
 1->
   >
 2 >            }
@@ -400,28 +400,28 @@ sourceFile:recursiveClassReferenceTest.ts
 4 >               Find
 5 >                   
 6 >                      Find
-7 >                                   
-8 >                                        Find
-9 >                                                      {
-  >                                                     	export class StartFindAction implements Sample.Thing.IAction {
-  >                                                     		
-  >                                                     		public getId() { return "yo"; }
-  >                                                     		
-  >                                                     		public run(Thing:Sample.Thing.ICodeThing):boolean {
-  >                                                     
-  >                                                     			return true;
-  >                                                     		}
-  >                                                     	}
-  >                                                     }
+7 >                                  
+8 >                                       Find
+9 >                                                    {
+  >                                                   	export class StartFindAction implements Sample.Thing.IAction {
+  >                                                   		
+  >                                                   		public getId() { return "yo"; }
+  >                                                   		
+  >                                                   		public run(Thing:Sample.Thing.ICodeThing):boolean {
+  >                                                   
+  >                                                   			return true;
+  >                                                   		}
+  >                                                   	}
+  >                                                   }
 1->Emitted(29, 13) Source(42, 1) + SourceIndex(0) name (Sample.Actions.Thing.Find)
 2 >Emitted(29, 14) Source(42, 2) + SourceIndex(0) name (Sample.Actions.Thing.Find)
 3 >Emitted(29, 16) Source(32, 29) + SourceIndex(0) name (Sample.Actions.Thing)
 4 >Emitted(29, 20) Source(32, 33) + SourceIndex(0) name (Sample.Actions.Thing)
 5 >Emitted(29, 23) Source(32, 29) + SourceIndex(0) name (Sample.Actions.Thing)
-6 >Emitted(29, 36) Source(32, 33) + SourceIndex(0) name (Sample.Actions.Thing)
-7 >Emitted(29, 41) Source(32, 29) + SourceIndex(0) name (Sample.Actions.Thing)
-8 >Emitted(29, 54) Source(32, 33) + SourceIndex(0) name (Sample.Actions.Thing)
-9 >Emitted(29, 62) Source(42, 2) + SourceIndex(0) name (Sample.Actions.Thing)
+6 >Emitted(29, 35) Source(32, 33) + SourceIndex(0) name (Sample.Actions.Thing)
+7 >Emitted(29, 40) Source(32, 29) + SourceIndex(0) name (Sample.Actions.Thing)
+8 >Emitted(29, 52) Source(32, 33) + SourceIndex(0) name (Sample.Actions.Thing)
+9 >Emitted(29, 60) Source(42, 2) + SourceIndex(0) name (Sample.Actions.Thing)
 ---
 >>>        })(Thing = Actions.Thing || (Actions.Thing = {}));
 1 >^^^^^^^^
diff --git a/tests/baselines/reference/recursiveCloduleReference.js b/tests/baselines/reference/recursiveCloduleReference.js
index 5cb6e6b2c1e1b..74072e653ef9f 100644
--- a/tests/baselines/reference/recursiveCloduleReference.js
+++ b/tests/baselines/reference/recursiveCloduleReference.js
@@ -20,8 +20,8 @@ var M;
     })();
     M.C = C;
     var C;
-    (function (_C) {
-        _C.C = M.C;
+    (function (C_1) {
+        C_1.C = M.C;
     })(C = M.C || (M.C = {}));
     ;
 })(M || (M = {}));
diff --git a/tests/baselines/reference/shadowingViaLocalValue.js b/tests/baselines/reference/shadowingViaLocalValue.js
index e788caf5720c1..0a589f8d427fd 100644
--- a/tests/baselines/reference/shadowingViaLocalValue.js
+++ b/tests/baselines/reference/shadowingViaLocalValue.js
@@ -17,13 +17,13 @@
 
 //// [shadowingViaLocalValue.js]
 {
-    var _x;
+    var x_1;
     {
         var x = 1;
     }
 }
 {
-    var _x1;
+    var x1_1;
     {
         for (var x1 = 0;;)
             ;
diff --git a/tests/baselines/reference/shadowingViaLocalValueOrBindingElement.js b/tests/baselines/reference/shadowingViaLocalValueOrBindingElement.js
index 594ec1ca18e81..a930f7405fff9 100644
--- a/tests/baselines/reference/shadowingViaLocalValueOrBindingElement.js
+++ b/tests/baselines/reference/shadowingViaLocalValueOrBindingElement.js
@@ -12,7 +12,7 @@ if (true) {
 
 //// [shadowingViaLocalValueOrBindingElement.js]
 if (true) {
-    var _x;
+    var x_1;
     if (true) {
         var x = 0; // Error
         var _a = ({
diff --git a/tests/baselines/reference/thisInModuleFunction1.js b/tests/baselines/reference/thisInModuleFunction1.js
index 1f46855239ab8..614ae58c86f65 100644
--- a/tests/baselines/reference/thisInModuleFunction1.js
+++ b/tests/baselines/reference/thisInModuleFunction1.js
@@ -8,10 +8,10 @@ var z = bar.bar();
 
 //// [thisInModuleFunction1.js]
 var bar;
-(function (_bar) {
+(function (bar_1) {
     function bar() {
         return this;
     }
-    _bar.bar = bar;
+    bar_1.bar = bar;
 })(bar || (bar = {}));
 var z = bar.bar();
diff --git a/tests/cases/compiler/letKeepNamesOfTopLevelItems.ts b/tests/cases/compiler/letKeepNamesOfTopLevelItems.ts
new file mode 100644
index 0000000000000..b5fc5fc031c2e
--- /dev/null
+++ b/tests/cases/compiler/letKeepNamesOfTopLevelItems.ts
@@ -0,0 +1,8 @@
+let x;
+function foo() {
+    let x;
+}
+
+module A {
+    let x;
+}
\ No newline at end of file
diff --git a/tests/cases/compiler/letShadowedByNameInNestedScope.ts b/tests/cases/compiler/letShadowedByNameInNestedScope.ts
new file mode 100644
index 0000000000000..e8b3e67322465
--- /dev/null
+++ b/tests/cases/compiler/letShadowedByNameInNestedScope.ts
@@ -0,0 +1,8 @@
+var x;
+function foo() {
+    let x = 0;
+    (function () {
+        var _x = 1;
+        console.log(x);
+    })();
+}
\ No newline at end of file