mirror of https://github.com/webpack/webpack.git
78 lines
2.1 KiB
JavaScript
78 lines
2.1 KiB
JavaScript
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/*
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MIT License http://www.opensource.org/licenses/mit-license.php
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Author Tobias Koppers @sokra
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*/
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"use strict";
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const mergeCache = new WeakMap();
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/**
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* Merges two given objects and caches the result to avoid computation if same objects passed as arguments again.
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* @example
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* // performs cleverMerge(first, second), stores the result in WeakMap and returns result
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* cachedCleverMerge({a: 1}, {a: 2})
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* {a: 2}
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* // when same arguments passed, gets the result from WeakMap and returns it.
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* cachedCleverMerge({a: 1}, {a: 2})
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* {a: 2}
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* @param {object} first first object
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* @param {object} second second object
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* @returns {object} merged object of first and second object
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*/
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const cachedCleverMerge = (first, second) => {
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let innerCache = mergeCache.get(first);
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if (innerCache === undefined) {
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innerCache = new WeakMap();
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mergeCache.set(first, innerCache);
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}
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const prevMerge = innerCache.get(second);
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if (prevMerge !== undefined) return prevMerge;
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const newMerge = cleverMerge(first, second);
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innerCache.set(second, newMerge);
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return newMerge;
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};
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/**
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* Merges two objects. Objects are not deeply merged.
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* TODO webpack 5: merge objects deeply clever.
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* Arrays might reference the old value with "..."
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* @param {object} first first object
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* @param {object} second second object
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* @returns {object} merged object of first and second object
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*/
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const cleverMerge = (first, second) => {
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const newObject = Object.assign({}, first);
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for (const key of Object.keys(second)) {
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if (!(key in newObject)) {
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newObject[key] = second[key];
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continue;
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}
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const secondValue = second[key];
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if (!Array.isArray(secondValue)) {
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newObject[key] = secondValue;
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continue;
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}
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const firstValue = newObject[key];
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if (Array.isArray(firstValue)) {
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const newArray = [];
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for (const item of secondValue) {
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if (item === "...") {
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for (const item of firstValue) {
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newArray.push(item);
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}
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} else {
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newArray.push(item);
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}
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}
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newObject[key] = newArray;
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} else {
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newObject[key] = secondValue;
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}
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}
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return newObject;
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};
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exports.cachedCleverMerge = cachedCleverMerge;
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exports.cleverMerge = cleverMerge;
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