webpack/lib/optimize/AggressiveMergingPlugin.js

/*
	MIT License http://www.opensource.org/licenses/mit-license.php
	Author Tobias Koppers @sokra
*/
"use strict";

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(compiler) {
		const options = this.options;
		const minSizeReduce = options.minSizeReduce || 1.5;

		compiler.hooks.thisCompilation.tap("AggressiveMergingPlugin", (compilation) => {
			compilation.hooks.optimizeChunksAdvanced.tap("AggressiveMergingPlugin", (chunks) => {
				let combinations = [];
				chunks.forEach((a, idx) => {
					if(a.canBeInitial()) return;
					for(let i = 0; i < idx; i++) {
						const b = chunks[i];
						if(b.canBeInitial()) continue;
						combinations.push({
							a,
							b,
							improvement: undefined
						});
					}
				});

				for(const pair of combinations) {
					const a = pair.b.size({
						chunkOverhead: 0
					});
					const b = pair.a.size({
						chunkOverhead: 0
					});
					const ab = pair.b.integratedSize(pair.a, {
						chunkOverhead: 0
					});
					let newSize;
					if(ab === false) {
						pair.improvement = false;
						return;
					} else {
						newSize = ab;
					}

					pair.improvement = (a + b) / newSize;
				}
				combinations = combinations.filter((pair) => {
					return pair.improvement !== false;
				});
				combinations.sort((a, b) => {
					return b.improvement - a.improvement;
				});

				const pair = combinations[0];

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

				if(pair.b.integrate(pair.a, "aggressive-merge")) {
					chunks.splice(chunks.indexOf(pair.a), 1);
					return true;
				}
			});
		});
	}
}

module.exports = AggressiveMergingPlugin;