[Breaking] ensure Error objects compare properly

Author: khirayama

.eslintrc

@@ -16,6 +16,7 @@
       "files": ["example/**", "test/**"],
       "rules": {
         "array-bracket-newline": 0,
+        "max-lines": 0,
         "max-statements": 0,
         "no-console": 0,
         "no-magic-numbers": 0,

index.js

@@ -50,7 +50,7 @@ function isBuffer(x) {
 }
 
 function objEquiv(a, b, opts) {
-  /* eslint max-statements: [2, 50] */
+  /* eslint max-statements: [2, 70] */
   var i, key;
   if (isUndefinedOrNull(a) || isUndefinedOrNull(b)) { return false; }
 
@@ -59,6 +59,13 @@ function objEquiv(a, b, opts) {
 
   if (isArguments(a) !== isArguments(b)) { return false; }
 
+  var aIsError = a instanceof Error;
+  var bIsError = b instanceof Error;
+  if (aIsError !== bIsError) { return false; }
+  if (aIsError || bIsError) {
+    if (a.name !== b.name || a.message !== b.message) { return false; }
+  }
+
   var aIsRegex = isRegex(a);
   var bIsRegex = isRegex(b);
   if (aIsRegex !== bIsRegex) { return false; }

test/cmp.js

@@ -316,3 +316,16 @@ test('arrays and objects', function (t) {
 
   t.end();
 });
+
+test('Errors', function (t) {
+  t.ok(equal(new Error('xyz'), new Error('xyz')), 'two errors of the same type with the same message are equal');
+  t.ok(equal(new Error('xyz'), new Error('xyz'), { strict: true }), 'strict: two errors of the same type with the same message are equal');
+
+  t.notOk(equal(new Error('xyz'), new TypeError('xyz')), 'two errors of different types with the same message are not equal');
+  t.notOk(equal(new TypeError('xyz'), new Error('xyz'), { strict: true }), 'strict: two errors of different types with the same message are not equal');
+
+  t.notOk(equal(new Error('xyz'), new Error('zyx')), 'two errors of the same type with a different message are not equal');
+  t.notOk(equal(new Error('xyz'), new Error('zyx'), { strict: true }), 'strict: two errors of the same type with a different message are not equal');
+
+  t.end();
+});