sveltejs · Conduitry · Jan 13, 2020 · Dec 10, 2019 · Jan 11, 2020 · Jan 11, 2020
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -2,6 +2,7 @@
 
 ## Unreleased
 
+* Remove old `<head>` elements during hydration so they aren't duplicated ([#1607](https://github.com/sveltejs/svelte/issues/1607))
 * Prevent text input cursor jumping in Safari with one-way binding ([#3449](https://github.com/sveltejs/svelte/issues/3449))
 * Expose compiler version in dev events ([#4047](https://github.com/sveltejs/svelte/issues/4047))
 * Don't run actions before their element is in the document ([#4166](https://github.com/sveltejs/svelte/issues/4166))

diff --git a/src/compiler/compile/css/Stylesheet.ts b/src/compiler/compile/css/Stylesheet.ts
@@ -5,6 +5,7 @@ import Element from '../nodes/Element';
 import { Ast, TemplateNode } from '../../interfaces';
 import Component from '../Component';
 import { CssNode } from './interfaces';
+import hash from "../utils/hash";
 
 function remove_css_prefix(name: string): string {
 	return name.replace(/^-((webkit)|(moz)|(o)|(ms))-/, '');
@@ -37,15 +38,6 @@ function minify_declarations(
 	return c;
 }
 
-// https://github.com/darkskyapp/string-hash/blob/master/index.js
-function hash(str: string): string {
-	let hash = 5381;
-	let i = str.length;
-
-	while (i--) hash = ((hash << 5) - hash) ^ str.charCodeAt(i);
-	return (hash >>> 0).toString(36);
-}
-
 class Rule {
 	selectors: Selector[];
 	declarations: Declaration[];

diff --git a/src/compiler/compile/nodes/Head.ts b/src/compiler/compile/nodes/Head.ts
@@ -1,9 +1,11 @@
 import Node from './shared/Node';
 import map_children from './shared/map_children';
+import hash from '../utils/hash';
 
 export default class Head extends Node {
 	type: 'Head';
 	children: any[]; // TODO
+	id: string;
 
 	constructor(component, parent, scope, info) {
 		super(component, parent, scope, info);
@@ -18,5 +20,9 @@ export default class Head extends Node {
 		this.children = map_children(component, parent, scope, info.children.filter(child => {
 			return (child.type !== 'Text' || /\S/.test(child.data));
 		}));
+
+		if (this.children.length > 0) {
+			this.id = `svelte-${hash(this.component.source.slice(this.start, this.end))}`;
+		}
 	}
 }
diff --git a/src/compiler/compile/render_dom/wrappers/Head.ts b/src/compiler/compile/render_dom/wrappers/Head.ts
@@ -3,11 +3,12 @@ import Renderer from '../Renderer';
 import Block from '../Block';
 import Head from '../../nodes/Head';
 import FragmentWrapper from './Fragment';
-import { x } from 'code-red';
+import { x, b } from 'code-red';
 import { Identifier } from 'estree';
 
 export default class HeadWrapper extends Wrapper {
 	fragment: FragmentWrapper;
+	node: Head;
 
 	constructor(
 		renderer: Renderer,
@@ -32,6 +33,18 @@ export default class HeadWrapper extends Wrapper {
 	}
 
 	render(block: Block, _parent_node: Identifier, _parent_nodes: Identifier) {
-		this.fragment.render(block, x`@_document.head` as unknown as Identifier, x`#nodes` as unknown as Identifier);
+		let nodes;
+		if (this.renderer.options.hydratable && this.fragment.nodes.length) {
+			nodes = block.get_unique_name('head_nodes');
+			block.chunks.claim.push(b`const ${nodes} = @query_selector_all('[data-svelte="${this.node.id}"]', @_document.head);`);
+		}
+
+		this.fragment.render(block, x`@_document.head` as unknown as Identifier, nodes);
+
+		if (nodes && this.renderer.options.hydratable) {
+			block.chunks.claim.push(
+				b`${nodes}.forEach(@detach);`
+			);
+		}
 	}
 }
diff --git a/src/compiler/compile/render_ssr/Renderer.ts b/src/compiler/compile/render_ssr/Renderer.ts
@@ -41,6 +41,7 @@ const handlers: Record<string, Handler> = {
 
 export interface RenderOptions extends CompileOptions{
 	locate: (c: number) => { line: number; column: number };
+	head_id?: string;
 }
 
 export default class Renderer {

diff --git a/src/compiler/compile/render_ssr/handlers/Element.ts b/src/compiler/compile/render_ssr/handlers/Element.ts
@@ -124,6 +124,10 @@ export default function(node: Element, renderer: Renderer, options: RenderOption
 		}
 	});
 
+	if (options.head_id) {
+		renderer.add_string(` data-svelte="${options.head_id}"`);
+	}
+
 	renderer.add_string('>');
 
 	if (node_contents !== undefined) {

diff --git a/src/compiler/compile/render_ssr/handlers/Head.ts b/src/compiler/compile/render_ssr/handlers/Head.ts
@@ -3,8 +3,13 @@ import Head from '../../nodes/Head';
 import { x } from 'code-red';
 
 export default function(node: Head, renderer: Renderer, options: RenderOptions) {
+	const head_options = {
+		...options,
+		head_id: node.id
+	};
+
 	renderer.push();
-	renderer.render(node.children, options);
+	renderer.render(node.children, head_options);
 	const result = renderer.pop();
 
 	renderer.add_expression(x`($$result.head += ${result}, "")`);

diff --git a/src/compiler/compile/render_ssr/handlers/Title.ts b/src/compiler/compile/render_ssr/handlers/Title.ts
@@ -5,7 +5,7 @@ import { x } from 'code-red';
 export default function(node: Title, renderer: Renderer, options: RenderOptions) {
 	renderer.push();
 
-	renderer.add_string(`<title>`);
+	renderer.add_string(`<title data-svelte="${options.head_id}">`);
 
 	renderer.render(node.children, options);
 

diff --git a/src/compiler/compile/utils/hash.ts b/src/compiler/compile/utils/hash.ts
@@ -0,0 +1,8 @@
+// https://github.com/darkskyapp/string-hash/blob/master/index.js
+export default function hash(str: string): string {
+	let hash = 5381;
+	let i = str.length;
+
+	while (i--) hash = ((hash << 5) - hash) ^ str.charCodeAt(i);
+	return (hash >>> 0).toString(36);
+}
diff --git a/src/runtime/internal/dom.ts b/src/runtime/internal/dom.ts
@@ -273,6 +273,10 @@ export function custom_event<T=any>(type: string, detail?: T) {
 	return e;
 }
 
+export function query_selector_all(selector: string, parent: HTMLElement = document.body) {
+	return Array.from(parent.querySelectorAll(selector));
+}
+
 export class HtmlTag {
 	e: HTMLElement;
 	n: ChildNode[];

diff --git a/test/helpers.js b/test/helpers.js
@@ -68,6 +68,7 @@ window.scrollTo = function(pageXOffset, pageYOffset) {
 
 export function env() {
 	window.document.title = '';
+	window.document.head.innerHTML = '';
 	window.document.body.innerHTML = '<main></main>';
 
 	return window;

diff --git a/test/hydration/index.js b/test/hydration/index.js
@@ -67,8 +67,16 @@ describe('hydration', () => {
 				}
 
 				const target = window.document.body;
+				const head = window.document.head;
+
 				target.innerHTML = fs.readFileSync(`${cwd}/_before.html`, 'utf-8');
 
+				let before_head;
+				try {
+					before_head = fs.readFileSync(`${cwd}/_before_head.html`, 'utf-8');
+					head.innerHTML = before_head;
+				} catch (err) {}
+
 				const snapshot = config.snapshot ? config.snapshot(target) : {};
 
 				const component = new SvelteComponent({
@@ -88,6 +96,19 @@ describe('hydration', () => {
 					}
 				}
 
+				if (before_head) {
+					try {
+						assert.htmlEqual(head.innerHTML, fs.readFileSync(`${cwd}/_after_head.html`, 'utf-8'));
+					} catch (error) {
+						if (shouldUpdateExpected()) {
+							fs.writeFileSync(`${cwd}/_after_head.html`, head.innerHTML);
+							console.log(`Updated ${cwd}/_after_head.html.`);
+						} else {
+							throw error;
+						}
+					}
+				}
+
 				if (config.test) {
 					config.test(assert, target, snapshot, component, window);
 				} else {

diff --git a/test/hydration/samples/head-meta-hydrate-duplicate/_after.html b/test/hydration/samples/head-meta-hydrate-duplicate/_after.html
@@ -0,0 +1 @@
+<div>Just a dummy page.</div>
diff --git a/test/hydration/samples/head-meta-hydrate-duplicate/_after_head.html b/test/hydration/samples/head-meta-hydrate-duplicate/_after_head.html
@@ -0,0 +1,4 @@
+<title>Some Title</title>
+<link href="/" rel="canonical">
+<meta content="some description" name="description">
+<meta content="some keywords" name="keywords">
diff --git a/test/hydration/samples/head-meta-hydrate-duplicate/_before.html b/test/hydration/samples/head-meta-hydrate-duplicate/_before.html
@@ -0,0 +1 @@
+<div>Just a dummy page.</div>
diff --git a/test/hydration/samples/head-meta-hydrate-duplicate/_before_head.html b/test/hydration/samples/head-meta-hydrate-duplicate/_before_head.html
@@ -0,0 +1,4 @@
+<title data-svelte="svelte-1s8aodm">Some Title</title>
+<link rel="canonical" href="/" data-svelte="svelte-1s8aodm">
+<meta name="description" content="some description" data-svelte="svelte-1s8aodm">
+<meta name="keywords" content="some keywords" data-svelte="svelte-1s8aodm">
diff --git a/test/hydration/samples/head-meta-hydrate-duplicate/_config.js b/test/hydration/samples/head-meta-hydrate-duplicate/_config.js
@@ -0,0 +1,5 @@
+export default {
+	test(assert, target, snapshot, component, window) {
+		assert.equal(window.document.querySelectorAll('meta').length, 2);
+	}
+};
diff --git a/test/hydration/samples/head-meta-hydrate-duplicate/main.svelte b/test/hydration/samples/head-meta-hydrate-duplicate/main.svelte
@@ -0,0 +1,8 @@
+<svelte:head>
+  <title>Some Title</title>
+  <link rel="canonical" href="/">
+  <meta name="description" content="some description">
+  <meta name="keywords" content="some keywords">
+</svelte:head>
+
+<div>Just a dummy page.</div>
diff --git a/test/server-side-rendering/samples/head-meta-hydrate-duplicate/_expected-head.html b/test/server-side-rendering/samples/head-meta-hydrate-duplicate/_expected-head.html
@@ -0,0 +1,4 @@
+<title data-svelte="svelte-1s8aodm">Some Title</title>
+<link rel="canonical" href="/" data-svelte="svelte-1s8aodm">
+<meta name="description" content="some description" data-svelte="svelte-1s8aodm">
+<meta name="keywords" content="some keywords" data-svelte="svelte-1s8aodm">
diff --git a/test/server-side-rendering/samples/head-meta-hydrate-duplicate/_expected.html b/test/server-side-rendering/samples/head-meta-hydrate-duplicate/_expected.html
@@ -0,0 +1,3 @@
+
+
+<div>Just a dummy page.</div>
diff --git a/test/server-side-rendering/samples/head-meta-hydrate-duplicate/main.svelte b/test/server-side-rendering/samples/head-meta-hydrate-duplicate/main.svelte
@@ -0,0 +1,8 @@
+<svelte:head>
+  <title>Some Title</title>
+  <link rel="canonical" href="/">
+  <meta name="description" content="some description">
+  <meta name="keywords" content="some keywords">
+</svelte:head>
+
+<div>Just a dummy page.</div>
diff --git a/test/server-side-rendering/samples/head-multiple-title/_expected-head.html b/test/server-side-rendering/samples/head-multiple-title/_expected-head.html
@@ -1 +1 @@
-<title>B</title>
+<title data-svelte="svelte-1csszk6">B</title>
diff --git a/test/server-side-rendering/samples/head-title/_expected-head.html b/test/server-side-rendering/samples/head-title/_expected-head.html
@@ -1 +1 @@
-<title>a custom title</title>
+<title data-svelte="svelte-135agoq">a custom title</title>