mapObject.js

/**
 * Copyright 2013-2014, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 *
 * @providesModule mapObject
 */

'use strict';

var hasOwnProperty = Object.prototype.hasOwnProperty;

/**
 * Executes the provided `callback` once for each enumerable own property in the
 * object and constructs a new object from the results. The `callback` is
 * invoked with three arguments:
 *
 *  - the property value
 *  - the property name
 *  - the object being traversed
 *
 * Properties that are added after the call to `mapObject` will not be visited
 * by `callback`. If the values of existing properties are changed, the value
 * passed to `callback` will be the value at the time `mapObject` visits them.
 * Properties that are deleted before being visited are not visited.
 *
 * @grep function objectMap()
 * @grep function objMap()
 *
 * @param {?object} object
 * @param {function} callback
 * @param {*} context
 * @return {?object}
 */
function mapObject(object, callback, context) {
  if (!object) {
    return null;
  }
  var result = {};
  for (var name in object) {
    if (hasOwnProperty.call(object, name)) {
      result[name] = callback.call(context, object[name], name, object);
    }
  }
  return result;
}

module.exports = mapObject;