webpack/lib/prefetch/ChunkPreloadTriggerRuntimeModule.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("../RuntimeGlobals");
const RuntimeModule = require("../RuntimeModule");
const Template = require("../Template");

/** @typedef {import("../Compilation")} Compilation */
/** @typedef {import("../Chunk").ChunkChildIdsByOrdersMap} ChunkChildIdsByOrdersMap */

class ChunkPreloadTriggerRuntimeModule extends RuntimeModule {
	/**
	 * @param {ChunkChildIdsByOrdersMap} chunkMap map from chunk to chunks
	 * @param {string=} handlerKey the `ensureChunkHandlers` key to install under (default `"preload"`); `"cssPreload"` preloads only the CSS handler so it stays CSS-only even when the build also registers a JS preload handler
	 */
	constructor(chunkMap, handlerKey = "preload") {
		super(`chunk ${handlerKey} trigger`, RuntimeModule.STAGE_TRIGGER);
		/** @type {ChunkChildIdsByOrdersMap} */
		this.chunkMap = chunkMap;
		/** @type {string} */
		this.handlerKey = handlerKey;
	}

	/**
	 * Generates runtime code for this runtime module.
	 * @returns {string | null} runtime code
	 */
	generate() {
		const { chunkMap, handlerKey } = this;
		const compilation = /** @type {Compilation} */ (this.compilation);
		const { runtimeTemplate } = compilation;
		// `cssPreload` calls only the CSS preload handler (`preloadChunkHandlers.s`)
		// so it stays CSS-only regardless of a JS preload handler registered
		// elsewhere; plain `preload` fans out to every handler via `preloadChunk`.
		const body =
			handlerKey === "cssPreload"
				? [
						`var handler = ${RuntimeGlobals.preloadChunkHandlers}.s;`,
						"var chunks = chunkToChildrenMap[chunkId];",
						"if (handler && Array.isArray(chunks)) chunks.forEach(handler);"
					]
				: [
						"var chunks = chunkToChildrenMap[chunkId];",
						`Array.isArray(chunks) && chunks.map(${RuntimeGlobals.preloadChunk});`
					];
		return Template.asString([
			`var chunkToChildrenMap = ${JSON.stringify(chunkMap, null, "\t")};`,
			`${
				RuntimeGlobals.ensureChunkHandlers
			}.${handlerKey} = ${runtimeTemplate.basicFunction("chunkId", body)};`
		]);
	}
}

module.exports = ChunkPreloadTriggerRuntimeModule;