webpack/lib/cache/getLazyHashedEtag.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 createHash = require("../util/createHash");

/** @typedef {import("../util/Hash")} Hash */

/**
 * @typedef {Object} HashableObject
 * @property {function(Hash): void} updateHash
 */

class LazyHashedEtag {
	/**
	 * @param {HashableObject} obj object with updateHash method
	 */
	constructor(obj) {
		this._obj = obj;
		this._hash = undefined;
	}

	/**
	 * @returns {string} hash of object
	 */
	toString() {
		if (this._hash === undefined) {
			const hash = createHash("md4");
			this._obj.updateHash(hash);
			this._hash = /** @type {string} */ (hash.digest("base64"));
		}
		return this._hash;
	}
}

/** @type {WeakMap<HashableObject, LazyHashedEtag>} */
const map = new WeakMap();

/**
 * @param {HashableObject} obj object with updateHash method
 * @returns {LazyHashedEtag} etag
 */
const getter = obj => {
	const hash = map.get(obj);
	if (hash !== undefined) return hash;
	const newHash = new LazyHashedEtag(obj);
	map.set(obj, newHash);
	return newHash;
};

module.exports = getter;