index.js

var global = require('./lib/global');

/** Used as the `TypeError` message for "Functions" methods. */

/** Used as the `TypeError` message for "Functions" methods. */
var FUNC_ERROR_TEXT = 'Expected a function';

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

/** Used to check objects for own properties. */
var hasOwnProperty = objectProto.hasOwnProperty;

/**
 * Creates a cache object to store key/value pairs.
 *
 * @private
 * @static
 * @name Cache
 * @memberOf _.memoize
 */
function MapCache() {
  this.__data__ = {};
}

/**
 * Removes `key` and its value from the cache.
 *
 * @private
 * @name delete
 * @memberOf _.memoize.Cache
 * @param {string} key The key of the value to remove.
 * @returns {boolean} Returns `true` if the entry was removed successfully, else `false`.
 */
function mapDelete(key) {
  return this.has(key) && delete this.__data__[key];
}

/**
 * Gets the cached value for `key`.
 *
 * @private
 * @name get
 * @memberOf _.memoize.Cache
 * @param {string} key The key of the value to get.
 * @returns {*} Returns the cached value.
 */
function mapGet(key) {
  return key == '__proto__' ? undefined : this.__data__[key];
}

/**
 * Checks if a cached value for `key` exists.
 *
 * @private
 * @name has
 * @memberOf _.memoize.Cache
 * @param {string} key The key of the entry to check.
 * @returns {boolean} Returns `true` if an entry for `key` exists, else `false`.
 */
function mapHas(key) {
  return key != '__proto__' && hasOwnProperty.call(this.__data__, key);
}

/**
 * Sets `value` to `key` of the cache.
 *
 * @private
 * @name set
 * @memberOf _.memoize.Cache
 * @param {string} key The key of the value to cache.
 * @param {*} value The value to cache.
 * @returns {Object} Returns the cache object.
 */
function mapSet(key, value) {
  if (key != '__proto__') {
    this.__data__[key] = value;
  }
  return this;
}

/**
 * Creates a function that memoizes the result of `func`. If `resolver` is
 * provided it determines 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 coerced to a string and used as the
 * cache key. The `func` is invoked with the `this` binding of the memoized
 * function.
 *
 * **Note:** The cache is exposed as the `cache` property on the memoized
 * function. Its creation may be customized by replacing the `_.memoize.Cache`
 * constructor with one whose instances implement the [`Map`](http://ecma-international.org/ecma-262/6.0/#sec-properties-of-the-map-prototype-object)
 * method interface of `get`, `has`, and `set`.
 *
 * @static
 * @memberOf _
 * @category Function
 * @param {Function} func The function to have its output memoized.
 * @param {Function} [resolver] The function to resolve the cache key.
 * @returns {Function} Returns the new memoizing function.
 * @example
 *
 * var upperCase = _.memoize(function(string) {
 *   return string.toUpperCase();
 * });
 *
 * upperCase('fred');
 * // => 'FRED'
 *
 * // modifying the result cache
 * upperCase.cache.set('fred', 'BARNEY');
 * upperCase('fred');
 * // => 'BARNEY'
 *
 * // replacing `_.memoize.Cache`
 * var object = { 'user': 'fred' };
 * var other = { 'user': 'barney' };
 * var identity = _.memoize(_.identity);
 *
 * identity(object);
 * // => { 'user': 'fred' }
 * identity(other);
 * // => { 'user': 'fred' }
 *
 * _.memoize.Cache = WeakMap;
 * var identity = _.memoize(_.identity);
 *
 * identity(object);
 * // => { 'user': 'fred' }
 * identity(other);
 * // => { 'user': 'barney' }
 */
function memoize(func, resolver) {
  if (typeof func != 'function' || (resolver && typeof resolver != 'function')) {
    throw new TypeError(FUNC_ERROR_TEXT);
  }
  var args, key, cache;
  var memoized = function() {
    args = new Array(arguments.length);
    for (var i = 0, l = arguments.length; i < l; i++) {
      args[i] = arguments[i];
    }
    key = resolver ? resolver.apply(this, args) : args[0];
    cache = memoized.cache;

    if (cache.has(key)) {
      return cache.get(key);
    }
    var result = func.apply(this, args);
    memoized.cache = cache.set(key, result);
    return result;
  };
  memoized.cache = new memoize.Cache;
  return memoized;
}

// Add functions to the `Map` cache.
MapCache.prototype['delete'] = mapDelete;
MapCache.prototype.get = mapGet;
MapCache.prototype.has = mapHas;
MapCache.prototype.set = mapSet;

// Assign cache to `_.memoize`.
memoize.Cache = global.Map || MapCache;

module.exports = memoize;