webpack/lib/prefetch/StartupAssetHintRuntimeModule.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 RuntimeGlobals = require("../runtime/RuntimeGlobals");
const RuntimeModule = require("../runtime/RuntimeModule");
const Template = require("../template/Template");

/** @import Compilation from "../Compilation" */

/**
 * Fires `<link rel="prefetch">` / `<link rel="preload">` for every asset
 * referenced from this chunk via `new URL(..., import.meta.url)` carrying
 * `webpackPrefetch` / `webpackPreload`, at chunk startup. Runs before any
 * user module evaluates, so by the time user code reaches the
 * corresponding `new URL(...)` (or hands the URL to `<img>`, `fetch`,
 * `new Worker`, etc.), the browser already has the response in flight.
 *
 * The calls themselves are rendered by `ResourceHintPlugin`, while runtime
 * requirements are still open — see `collectStartupAssetHintLines`.
 */
class StartupAssetHintRuntimeModule extends RuntimeModule {
	/**
	 * @param {string[]} lines the `<link>` calls this chunk fires at startup
	 */
	constructor(lines) {
		super("startup asset hints", RuntimeModule.STAGE_TRIGGER);
		this._lines = lines;
	}

	/**
	 * The `[handlerMap, key]` pairs this module installs onto a chunk handler map
	 * such as `__webpack_require__.f`, or `null` where it cannot name them.
	 * @returns {[string, string][] | null} installed chunk handlers (do not mutate)
	 */
	getInstalledChunkHandlers() {
		return RuntimeModule.NO_CHUNK_HANDLERS;
	}

	/**
	 * Generates runtime code for this runtime module.
	 * @returns {string | null} runtime code
	 */
	generate() {
		const compilation = /** @type {Compilation} */ (this.compilation);
		const lines = this._lines;
		if (lines.length === 0) return null;
		// `__webpack_nonce__` set in the entry module comes too late, the entry not
		// having run, so the nonce is read off the `<script>` that loaded the bundle
		// and the links match a CSP demanding the script's own.

		// Classic output finds it on `document.currentScript`. ESM output leaves that
		// null, so the loading `<script type="module">` is found by matching its
		// `src` against `import.meta.url`.
		const { module: isModule, importMetaName } = compilation.outputOptions;
		const nonceSetup = isModule
			? [
					"if (typeof document !== 'undefined') {",
					Template.indent([
						`var url = ${importMetaName}.url;`,
						"var scripts = document.getElementsByTagName('script');",
						"for (var i = 0; i < scripts.length; i++) {",
						Template.indent([
							`if (scripts[i].src === url && scripts[i].nonce && !${RuntimeGlobals.scriptNonce}) {`,
							Template.indent([
								`${RuntimeGlobals.scriptNonce} = scripts[i].nonce;`,
								"break;"
							]),
							"}"
						]),
						"}"
					]),
					"}"
				]
			: [
					"if (typeof document !== 'undefined') {",
					Template.indent([
						"var currentScript = document.currentScript;",
						`if (currentScript && currentScript.nonce && !${RuntimeGlobals.scriptNonce}) {`,
						Template.indent(
							`${RuntimeGlobals.scriptNonce} = currentScript.nonce;`
						),
						"}"
					]),
					"}"
				];
		return Template.asString([...nonceSetup, ...lines]);
	}
}

module.exports = StartupAssetHintRuntimeModule;