Cloning an Object

JavaScript performance comparison

Revision 43 of this test case created by Jonathan Perry

Info

There is no quick and easy facility for cloning an object, Some people recommend using JQuery.extend others JSON.parse/stringify

http://stackoverflow.com/questions/122102/what-is-the-most-efficient-way-to-clone-a-javascript-object

If you want the fastest possible clone function. I would personally anticipate the data structure of your object and write a custom clone to handle it.

Preparation code

<script src="//ajax.googleapis.com/ajax/libs/jquery/1/jquery.min.js"></script>

<script src="//underscorejs.org/underscore-min.js"></script>
<script src="https://raw.github.com/jgallen23/aug/master/lib/aug.js"></script>
<script>
  var oldObject = {
   a: 1,
   b: 2,
   c: 3,
   d: 4,
   e: 5,
   f: function() {
    return 6;
   },
   g: [7, 8, 9]
  };
  var i = 1000;
  while (i--)
    oldObject[Math.random()] = i;
 
  function clone(obj) {
   var target = {};
   for (var i in obj) {
    if (obj.hasOwnProperty(i)) {
     target[i] = obj[i];
    }
   }
   return target;
  }
var extendA = function(source, target) {
    var keys = Object.keys(source),
        i = keys.length,
        target = target || {};
    while (i--) {
        target[keys[i]] = source[keys[i]];
    }
    return target;
}

var extendB = function(source, target) {
    var keys = Object.keys(source),
        i = keys.length,
        k,
        target = target || {};
    while (i--) {
        k = keys[i];
        target[k] = source[k];
    }
    return target;
}

var extendC = function(source, target) {
    var keys = Object.keys(source),
        i = keys.length - 1,
        k,
        target = target || {};
    do {
        k = keys[i];
        target[k] = source[k];
    }
    while (i--);
    return target;
}

  Object.defineProperties(Object, {
   'extend': {
    'configurable': true,
    'enumerable': false,
    'value': function extend(what, wit) {
     var extObj, witKeys = Object.keys(wit);
 
     extObj = Object.keys(what).length ? Object.clone(what) : {};
 
     witKeys.forEach(function(key) {
      Object.defineProperty(extObj, key, Object.getOwnPropertyDescriptor(wit, key));
     });
 
     return extObj;
    },
    'writable': true
   },
   'clone': {
    'configurable': true,
    'enumerable': false,
    'value': function clone(obj) {
     return Object.extend({}, obj);
    },
    'writable': true
   }
  });
</script>

Preparation code output

Test runner

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Testing in unknown unknown
Test Ops/sec
JQuery.extend deep
var newObject = jQuery.extend(true, {}, oldObject);
pending…
JSON
var newObject = JSON.parse(JSON.stringify(oldObject));
pending…
JQuery.extend
var newObject = jQuery.extend({}, oldObject);
pending…
simple clone function
var newObject = clone(oldObject);
pending…
ES5 Object.clone
var newObject = Object.clone(oldObject);
pending…
efficient extend
var newObject = extendA(oldObject);
pending…
underscore clone
var newObject = _.clone(oldObject);
pending…
underscore extend
var newObject = _.extend({}, oldObject);
pending…
aug deep extend
var newObject = aug(true, {}, oldObject);
pending…
tweaked extend 1
var newObject = extendB(oldObject);
pending…
tweaked extend 2
var newObject = extendC(oldObject);
pending…

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Revisions

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