webpack/lib/optimize/AggressiveMergingPlugin.js

Packs CommonJs/AMD modules for the browser. Allows to split your codebase into multiple bundles, which can be loaded on demand. Support 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
	Author Tobias Koppers @sokra
*/

"use strict";

const { STAGE_ADVANCED } = require("../OptimizationStages");

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

class AggressiveMergingPlugin {
	constructor(options) {
		if (
			(options !== undefined && typeof options !== "object") ||
			Array.isArray(options)
		) {
			throw new Error(
				"Argument should be an options object. To use defaults, pass in nothing.\nFor more info on options, see https://webpack.js.org/plugins/"
			);
		}
		this.options = options || {};
	}

	/**
	 * Apply the plugin
	 * @param {Compiler} compiler the compiler instance
	 * @returns {void}
	 */
	apply(compiler) {
		const options = this.options;
		const minSizeReduce = options.minSizeReduce || 1.5;

		compiler.hooks.thisCompilation.tap(
			"AggressiveMergingPlugin",
			compilation => {
				compilation.hooks.optimizeChunks.tap(
					{
						name: "AggressiveMergingPlugin",
						stage: STAGE_ADVANCED
					},
					chunks => {
						const chunkGraph = compilation.chunkGraph;
						/** @type {{a: Chunk, b: Chunk, improvement: number}[]} */
						let combinations = [];
						for (const a of chunks) {
							if (a.canBeInitial()) continue;
							for (const b of chunks) {
								if (b.canBeInitial()) continue;
								if (b === a) break;
								if (!chunkGraph.canChunksBeIntegrated(a, b)) {
									continue;
								}
								const aSize = chunkGraph.getChunkSize(b, {
									chunkOverhead: 0
								});
								const bSize = chunkGraph.getChunkSize(a, {
									chunkOverhead: 0
								});
								const abSize = chunkGraph.getIntegratedChunksSize(b, a, {
									chunkOverhead: 0
								});
								const improvement = (aSize + bSize) / abSize;
								combinations.push({
									a,
									b,
									improvement
								});
							}
						}

						combinations.sort((a, b) => {
							return b.improvement - a.improvement;
						});

						const pair = combinations[0];

						if (!pair) return;
						if (pair.improvement < minSizeReduce) return;

						chunkGraph.integrateChunks(pair.b, pair.a);
						compilation.chunks.delete(pair.a);
						return true;
					}
				);
			}
		);
	}
}

module.exports = AggressiveMergingPlugin;