lodash.memoize/index.js

/**
 * Lo-Dash 2.2.0 (Custom Build) <http://lodash.com/>
 * Build: `lodash modularize modern exports="npm" -o ./npm`
 * Copyright 2012-2013 The Dojo Foundation <http://dojofoundation.org/>
 * Based on Underscore.js 1.5.2 <http://underscorejs.org/LICENSE>
 * Copyright 2009-2013 Jeremy Ashkenas, DocumentCloud and Investigative Reporters & Editors
 * Available under MIT license <http://lodash.com/license>
 */
var isFunction = require('lodash.isfunction'),
    keyPrefix = require('lodash._keyprefix');

/** Used for native method references */
var objectProto = Object.prototype;

/** Native method shortcuts */
var hasOwnProperty = objectProto.hasOwnProperty;

/**
 * Creates a function that memoizes the result of `func`. If `resolver` is
 * provided it will be used to determine the cache key for storing the result
 * based on the arguments provided to the memoized function. By default, the
 * first argument provided to the memoized function is used as the cache key.
 * The `func` is executed with the `this` binding of the memoized function.
 * The result cache is exposed as the `cache` property on the memoized function.
 *
 * @static
 * @memberOf _
 * @category Functions
 * @param {Function} func The function to have its output memoized.
 * @param {Function} [resolver] A function used to resolve the cache key.
 * @returns {Function} Returns the new memoizing function.
 * @example
 *
 * var fibonacci = _.memoize(function(n) {
 *   return n < 2 ? n : fibonacci(n - 1) + fibonacci(n - 2);
 * });
 *
 * var data = {
 *   'moe': { 'name': 'moe', 'age': 40 },
 *   'curly': { 'name': 'curly', 'age': 60 }
 * };
 *
 * // modifying the result cache
 * var stooge = _.memoize(function(name) { return data[name]; }, _.identity);
 * stooge('curly');
 * // => { 'name': 'curly', 'age': 60 }
 *
 * stooge.cache.curly.name = 'jerome';
 * stooge('curly');
 * // => { 'name': 'jerome', 'age': 60 }
 */
function memoize(func, resolver) {
  if (!isFunction(func)) {
    throw new TypeError;
  }
  var memoized = function() {
    var cache = memoized.cache,
        key = resolver ? resolver.apply(this, arguments) : keyPrefix + arguments[0];

    return hasOwnProperty.call(cache, key)
      ? cache[key]
      : (cache[key] = func.apply(this, arguments));
  }
  memoized.cache = {};
  return memoized;
}

module.exports = memoize;