memoize.js (2224B)
1 var MapCache = require('./_MapCache'); 2 3 /** Error message constants. */ 4 var FUNC_ERROR_TEXT = 'Expected a function'; 5 6 /** 7 * Creates a function that memoizes the result of `func`. If `resolver` is 8 * provided, it determines the cache key for storing the result based on the 9 * arguments provided to the memoized function. By default, the first argument 10 * provided to the memoized function is used as the map cache key. The `func` 11 * is invoked with the `this` binding of the memoized function. 12 * 13 * **Note:** The cache is exposed as the `cache` property on the memoized 14 * function. Its creation may be customized by replacing the `_.memoize.Cache` 15 * constructor with one whose instances implement the 16 * [`Map`](http://ecma-international.org/ecma-262/7.0/#sec-properties-of-the-map-prototype-object) 17 * method interface of `clear`, `delete`, `get`, `has`, and `set`. 18 * 19 * @static 20 * @memberOf _ 21 * @since 0.1.0 22 * @category Function 23 * @param {Function} func The function to have its output memoized. 24 * @param {Function} [resolver] The function to resolve the cache key. 25 * @returns {Function} Returns the new memoized function. 26 * @example 27 * 28 * var object = { 'a': 1, 'b': 2 }; 29 * var other = { 'c': 3, 'd': 4 }; 30 * 31 * var values = _.memoize(_.values); 32 * values(object); 33 * // => [1, 2] 34 * 35 * values(other); 36 * // => [3, 4] 37 * 38 * object.a = 2; 39 * values(object); 40 * // => [1, 2] 41 * 42 * // Modify the result cache. 43 * values.cache.set(object, ['a', 'b']); 44 * values(object); 45 * // => ['a', 'b'] 46 * 47 * // Replace `_.memoize.Cache`. 48 * _.memoize.Cache = WeakMap; 49 */ 50 function memoize(func, resolver) { 51 if (typeof func != 'function' || (resolver != null && typeof resolver != 'function')) { 52 throw new TypeError(FUNC_ERROR_TEXT); 53 } 54 var memoized = function() { 55 var args = arguments, 56 key = resolver ? resolver.apply(this, args) : args[0], 57 cache = memoized.cache; 58 59 if (cache.has(key)) { 60 return cache.get(key); 61 } 62 var result = func.apply(this, args); 63 memoized.cache = cache.set(key, result) || cache; 64 return result; 65 }; 66 memoized.cache = new (memoize.Cache || MapCache); 67 return memoized; 68 } 69 70 // Expose `MapCache`. 71 memoize.Cache = MapCache; 72 73 module.exports = memoize;