JavaScript: Object#forIn and Object#forOwn

object-forin-forown.js

/*
 * Object#forIn, Object#forOwn
 *
 * Copyright (c) 2012 "Cowboy" Ben Alman
 * Licensed under the MIT license.
 * http://benalman.com/about/license/
 */

Object.defineProperties(Object.prototype, {
  forIn: {
    writable: true,
    configurable: true,
    value: function(iterator, thisValue) {
      for (var prop in this) {
        iterator.call(thisValue, this[prop], prop, this);
      }
    }
  },
  forOwn: {
    writable: true,
    configurable: true,
    value: function(iterator, thisValue) {
      Object.keys(this).forEach(function(key) {
        iterator.call(thisValue, this[key], key, this);
      }, this);
    }
  }
});

var obj = {a: 1, b: 2};
var sub = Object.create(obj);
sub.c = 3;
sub.d = 4;

sub.forIn(console.log, console);
// 3 'c' { c: 3, d: 4 }
// 4 'd' { c: 3, d: 4 }
// 1 'a' { c: 3, d: 4 }
// 2 'b' { c: 3, d: 4 }

sub.forOwn(console.log, console);
// 3 'c' { c: 3, d: 4 }
// 4 'd' { c: 3, d: 4 }