optimise <title>

src/generators/Generator.ts

@@ -721,6 +721,14 @@ export default class Generator {
 		let indexes = new Set();
 		const indexesStack: Set<string>[] = [indexes];
 
+		function parentIsHead(node) {
+			if (!node) return false;
+			if (node.type === 'Component' || node.type === 'Element') return false;
+			if (node.type === 'Head') return true;
+
+			return parentIsHead(node.parent);
+		}
+
 		walk(html, {
 			enter(node: Node, parent: Node, key: string) {
 				// TODO this is hacky as hell
@@ -738,6 +746,9 @@ export default class Generator {
 				} else if (node.name === ':Head') { // TODO do this in parse?
 					node.type = 'Head';
 					Object.setPrototypeOf(node, nodes.Head.prototype);
+				} else if (node.type === 'Element' && node.name === 'title' && parentIsHead(parent)) { // TODO do this in parse?
+					node.type = 'Title';
+					Object.setPrototypeOf(node, nodes.Title.prototype);
 				} else if (node.type === 'Element' && node.name === 'slot' && !generator.customElement) {
 					node.type = 'Slot';
 					Object.setPrototypeOf(node, nodes.Slot.prototype);

src/generators/nodes/Title.ts

@@ -0,0 +1,98 @@
+import { stringify } from '../../utils/stringify';
+import getExpressionPrecedence from '../../utils/getExpressionPrecedence';
+import Node from './shared/Node';
+import Block from '../dom/Block';
+
+export default class Title extends Node {
+	build(
+		block: Block,
+		parentNode: string,
+		parentNodes: string
+	) {
+		const isDynamic = !!this.children.find(node => node.type !== 'Text');
+
+		if (isDynamic) {
+			let value;
+
+			const allDependencies = new Set();
+			let shouldCache;
+
+			// TODO some of this code is repeated in Tag.ts — would be good to
+			// DRY it out if that's possible without introducing crazy indirection
+			if (this.children.length === 1) {
+				// single {{tag}} — may be a non-string
+				const { expression } = this.children[0];
+				const { indexes } = block.contextualise(expression);
+				const { dependencies, snippet } = this.children[0].metadata;
+
+				value = snippet;
+				dependencies.forEach(d => {
+					allDependencies.add(d);
+				});
+
+				shouldCache = (
+					expression.type !== 'Identifier' ||
+					block.contexts.has(expression.name)
+				);
+			} else {
+				// '{{foo}} {{bar}}' — treat as string concatenation
+				value =
+					(this.children[0].type === 'Text' ? '' : `"" + `) +
+					this.children
+						.map((chunk: Node) => {
+							if (chunk.type === 'Text') {
+								return stringify(chunk.data);
+							} else {
+								const { indexes } = block.contextualise(chunk.expression);
+								const { dependencies, snippet } = chunk.metadata;
+
+								dependencies.forEach(d => {
+									allDependencies.add(d);
+								});
+
+								return getExpressionPrecedence(chunk.expression) <= 13 ? `(${snippet})` : snippet;
+							}
+						})
+						.join(' + ');
+
+				shouldCache = true;
+			}
+
+			const last = shouldCache && block.getUniqueName(
+				`title_value`
+			);
+
+			if (shouldCache) block.addVariable(last);
+
+			let updater;
+			const init = shouldCache ? `${last} = ${value}` : value;
+
+			block.builders.init.addLine(
+				`document.title = ${init};`
+			);
+			updater = `document.title = ${shouldCache ? last : value};`;
+
+			if (allDependencies.size) {
+				const dependencies = Array.from(allDependencies);
+				const changedCheck = (
+					( block.hasOutroMethod ? `#outroing || ` : '' ) +
+					dependencies.map(dependency => `changed.${dependency}`).join(' || ')
+				);
+
+				const updateCachedValue = `${last} !== (${last} = ${value})`;
+
+				const condition = shouldCache ?
+					( dependencies.length ? `(${changedCheck}) && ${updateCachedValue}` : updateCachedValue ) :
+					changedCheck;
+
+				block.builders.update.addConditional(
+					condition,
+					updater
+				);
+			}
+		} else {
+			const value = stringify(this.children[0].data);
+			block.builders.hydrate.addLine(`document.title = ${value};`);
+		}
+	}
+}

src/generators/nodes/index.ts

@@ -19,6 +19,7 @@ import Ref from './Ref';
 import Slot from './Slot';
 import Text from './Text';
 import ThenBlock from './ThenBlock';
+import Title from './Title';
 import Transition from './Transition';
 import Window from './Window';
 
@@ -43,6 +44,7 @@ const nodes: Record<string, any> = {
 	Slot,
 	Text,
 	ThenBlock,
+	Title,
 	Transition,
 	Window
 };

src/generators/server-side-rendering/visitors/Title.ts

@@ -0,0 +1,19 @@
+import { SsrGenerator } from '../index';
+import Block from '../Block';
+import { escape } from '../../../utils/stringify';
+import visit from '../visit';
+import { Node } from '../../../interfaces';
+
+export default function visitTitle(
+	generator: SsrGenerator,
+	block: Block,
+	node: Node
+) {
+	generator.append(`<title>`);
+
+	node.children.forEach((child: Node) => {
+		visit(generator, block, child);
+	});
+
+	generator.append(`</title>`);
+}

src/generators/server-side-rendering/visitors/index.ts

@@ -9,6 +9,7 @@ import MustacheTag from './MustacheTag';
 import RawMustacheTag from './RawMustacheTag';
 import Slot from './Slot';
 import Text from './Text';
+import Title from './Title';
 import Window from './Window';
 
 export default {
@@ -23,5 +24,6 @@ export default {
 	RawMustacheTag,
 	Slot,
 	Text,
+	Title,
 	Window
 };

src/validate/html/validateElement.ts

@@ -3,7 +3,7 @@ import validateEventHandler from './validateEventHandler';
 import validate, { Validator } from '../index';
 import { Node } from '../../interfaces';
 
-const svg = /^(?:altGlyph|altGlyphDef|altGlyphItem|animate|animateColor|animateMotion|animateTransform|circle|clipPath|color-profile|cursor|defs|desc|discard|ellipse|feBlend|feColorMatrix|feComponentTransfer|feComposite|feConvolveMatrix|feDiffuseLighting|feDisplacementMap|feDistantLight|feDropShadow|feFlood|feFuncA|feFuncB|feFuncG|feFuncR|feGaussianBlur|feImage|feMerge|feMergeNode|feMorphology|feOffset|fePointLight|feSpecularLighting|feSpotLight|feTile|feTurbulence|filter|font|font-face|font-face-format|font-face-name|font-face-src|font-face-uri|foreignObject|g|glyph|glyphRef|hatch|hatchpath|hkern|image|line|linearGradient|marker|mask|mesh|meshgradient|meshpatch|meshrow|metadata|missing-glyph|mpath|path|pattern|polygon|polyline|radialGradient|rect|set|solidcolor|stop|switch|symbol|text|textPath|title|tref|tspan|unknown|use|view|vkern)$/;
+const svg = /^(?:altGlyph|altGlyphDef|altGlyphItem|animate|animateColor|animateMotion|animateTransform|circle|clipPath|color-profile|cursor|defs|desc|discard|ellipse|feBlend|feColorMatrix|feComponentTransfer|feComposite|feConvolveMatrix|feDiffuseLighting|feDisplacementMap|feDistantLight|feDropShadow|feFlood|feFuncA|feFuncB|feFuncG|feFuncR|feGaussianBlur|feImage|feMerge|feMergeNode|feMorphology|feOffset|fePointLight|feSpecularLighting|feSpotLight|feTile|feTurbulence|filter|font|font-face|font-face-format|font-face-name|font-face-src|font-face-uri|foreignObject|g|glyph|glyphRef|hatch|hatchpath|hkern|image|line|linearGradient|marker|mask|mesh|meshgradient|meshpatch|meshrow|metadata|missing-glyph|mpath|path|pattern|polygon|polyline|radialGradient|rect|set|solidcolor|stop|switch|symbol|text|textPath|tref|tspan|unknown|use|view|vkern)$/;
 
 export default function validateElement(
 	validator: Validator,
@@ -61,6 +61,24 @@ export default function validateElement(
 		}
 	}
 
+	if (node.name === 'title') {
+		if (node.attributes.length > 0) {
+			validator.error(
+				`<title> cannot have attributes`,
+				node.attributes[0].start
+			);
+		}
+
+		node.children.forEach(child => {
+			if (child.type !== 'Text' && child.type !== 'MustacheTag') {
+				validator.error(
+					`<title> can only contain text and {{tags}}`,
+					child.start
+				);
+			}
+		});
+	}
+
 	let hasIntro: boolean;
 	let hasOutro: boolean;
 	let hasTransition: boolean;

src/validate/html/validateHead.ts

@@ -1,8 +1,16 @@
+import validateElement from './validateElement';
 import { Validator } from '../index';
 import { Node } from '../../interfaces';
 
 export default function validateHead(validator: Validator, node: Node, refs: Map<string, Node[]>, refCallees: Node[]) {
 	if (node.attributes.length) {
 		validator.error(`<:Head> should not have any attributes or directives`, node.start);
 	}
+
+	// TODO ensure only valid elements are included here
+
+	node.children.forEach(node => {
+		if (node.type !== 'Element') return; // TODO handle {{#if}} and friends?
+		validateElement(validator, node, refs, refCallees, [], []);
+	});
 }