webpack/lib/cache/mergeEtags.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
	Author Tobias Koppers @sokra
*/

"use strict";

/** @typedef {import("../Cache").Etag} Etag */

class MergedEtag {
	/**
	 * Creates an instance of MergedEtag.
	 * @param {Etag} a first
	 * @param {Etag} b second
	 */
	constructor(a, b) {
		this.a = a;
		this.b = b;
	}

	toString() {
		return `${this.a.toString()}|${this.b.toString()}`;
	}
}

/** @type {WeakMap<Etag, WeakMap<Etag, MergedEtag>>} */
const dualObjectMap = new WeakMap();
/** @type {WeakMap<Etag, WeakMap<Etag, MergedEtag>>} */
const objectStringMap = new WeakMap();

/**
 * Merges the provided values into a single result.
 * @param {Etag} a first
 * @param {Etag} b second
 * @returns {string | MergedEtag} result
 */
const mergeEtags = (a, b) => {
	if (typeof a === "string") {
		if (typeof b === "string") {
			return `${a}|${b}`;
		}
		const temp = b;
		b = a;
		a = temp;
	} else if (typeof b !== "string") {
		// both a and b are objects
		let map = dualObjectMap.get(a);
		if (map === undefined) {
			dualObjectMap.set(a, (map = new WeakMap()));
		}
		const mergedEtag = map.get(b);
		if (mergedEtag === undefined) {
			const newMergedEtag = new MergedEtag(a, b);
			map.set(b, newMergedEtag);
			return newMergedEtag;
		}
		return mergedEtag;
	}
	// a is object, b is string
	let map = objectStringMap.get(a);
	if (map === undefined) {
		objectStringMap.set(a, (map = new Map()));
	}
	const mergedEtag = map.get(b);
	if (mergedEtag === undefined) {
		const newMergedEtag = new MergedEtag(a, b);
		map.set(b, newMergedEtag);
		return newMergedEtag;
	}
	return mergedEtag;
};

module.exports = mergeEtags;