gree_leran/node_modules/webpack/lib/util/MapHelpers.js

37 lines
1.1 KiB
JavaScript

/*
MIT License http://www.opensource.org/licenses/mit-license.php
Author Tobias Koppers @sokra
*/
"use strict";
/**
* getOrInsert is a helper function for maps that allows you to get a value
* from a map if it exists, or insert a new value if it doesn't. If it value doesn't
* exist, it will be computed by the provided function.
*
* @template K
* @template V
* @param {Map<K, V>} map The map object to check
* @param {K} key The key to check
* @param {function(): V} computer function which will compute the value if it doesn't exist
* @returns {V} The value from the map, or the computed value
*
* @example
* ```js
* const map = new Map();
* const value = getOrInsert(map, "key", () => "value");
* console.log(value); // "value"
* ```
*/
exports.getOrInsert = (map, key, computer) => {
// Grab key from map
const value = map.get(key);
// If the value already exists, return it
if (value !== undefined) return value;
// Otherwise compute the value, set it in the map, and return it
const newValue = computer();
map.set(key, newValue);
return newValue;
};