webpack/lib/prefetch/ResourceHintRuntimeModule.js

Packs ECMAScript/CommonJs/AMD modules for the browser. Allows you to split your codebase into multiple bundles, which can be loaded on demand. Supports loaders to preprocess files, i.e. json, jsx, es7, css, less, ... and your custom stuff.

/*
	MIT License http://www.opensource.org/licenses/mit-license.php
*/

"use strict";

const { SyncWaterfallHook } = require("tapable");
const Compilation = require("../Compilation");
const RuntimeGlobals = require("../RuntimeGlobals");
const RuntimeModule = require("../RuntimeModule");
const Template = require("../Template");
const { guessAsAttribute } = require("./parseResourceHintOptions");

/**
 * @typedef {object} ResourceHintRuntimeModulePluginHooks
 * @property {SyncWaterfallHook<[string]>} linkPrefetch
 * @property {SyncWaterfallHook<[string]>} linkPreload
 */

/** @type {WeakMap<Compilation, ResourceHintRuntimeModulePluginHooks>} */
const compilationHooksMap = new WeakMap();

class ResourceHintRuntimeModule extends RuntimeModule {
	/**
	 * @param {Compilation} compilation the compilation
	 * @returns {ResourceHintRuntimeModulePluginHooks} hooks
	 */
	static getCompilationHooks(compilation) {
		if (!(compilation instanceof Compilation)) {
			throw new TypeError(
				"The 'compilation' argument must be an instance of Compilation"
			);
		}
		let hooks = compilationHooksMap.get(compilation);
		if (hooks === undefined) {
			hooks = {
				linkPrefetch: new SyncWaterfallHook(["source"]),
				linkPreload: new SyncWaterfallHook(["source"])
			};
			compilationHooksMap.set(compilation, hooks);
		}
		return hooks;
	}

	/**
	 * @param {"prefetch" | "preload"} rel link rel value
	 */
	constructor(rel) {
		super(`asset ${rel}`, RuntimeModule.STAGE_ATTACH);
		this._rel = rel;
	}

	/**
	 * Generates runtime code for this runtime module.
	 * @returns {string | null} runtime code
	 */
	generate() {
		const compilation = /** @type {Compilation} */ (this.compilation);
		const { runtimeTemplate, outputOptions } = compilation;
		const { crossOriginLoading } = outputOptions;
		const isNeutralPlatform = runtimeTemplate.isNeutralPlatform();
		const rel = this._rel;
		const fnName =
			rel === "prefetch"
				? RuntimeGlobals.prefetchAsset
				: RuntimeGlobals.preloadAsset;
		const hook =
			ResourceHintRuntimeModule.getCompilationHooks(compilation)[
				rel === "prefetch" ? "linkPrefetch" : "linkPreload"
			];

		const body = [
			"if (installed[href]) return href;",
			"installed[href] = 1;",
			hook.call(
				Template.asString([
					"var link = document.createElement('link');",
					`link.rel = ${JSON.stringify(rel)};`,
					"link.href = href;",
					"if (as) link.as = as;",
					"if (type) link.type = type;",
					"if (media) link.media = media;",
					"if (fetchPriority) {",
					Template.indent([
						'link.setAttribute("fetchpriority", fetchPriority);'
					]),
					"}",
					`if (${RuntimeGlobals.scriptNonce}) {`,
					Template.indent(
						`link.setAttribute("nonce", ${RuntimeGlobals.scriptNonce});`
					),
					"}",
					crossOriginLoading
						? crossOriginLoading === "use-credentials"
							? 'link.crossOrigin = "use-credentials";'
							: Template.asString([
									"if (link.href.indexOf(window.location.origin + '/') !== 0) {",
									Template.indent(
										`link.crossOrigin = ${JSON.stringify(crossOriginLoading)};`
									),
									"}"
								])
						: ""
				])
			),
			"document.head.appendChild(link);",
			"return href;"
		];

		const fnBody = isNeutralPlatform
			? ["if (typeof document === 'undefined') return href;", ...body]
			: body;

		// `Object.create(null)` keeps the dedupe map free of inherited
		// properties (`toString`, `__proto__`, …) so any URL string is a
		// safe key.
		return Template.asString([
			"var installed = Object.create(null);",
			`${fnName} = ${runtimeTemplate.basicFunction(
				"href, as, type, media, fetchPriority",
				fnBody
			)};`
		]);
	}
}

ResourceHintRuntimeModule.guessAsAttribute = guessAsAttribute;

module.exports = ResourceHintRuntimeModule;