cloning an object

JavaScript performance comparison

Revision 12 of this test case created by David Mulder


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

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=""></script>
Benchmark.prototype.setup = function() {
    var oldObject = {
       a: 1,
       b: 2,
       c: 3,
       d: 4,
       e: 5,
       f: function() {
        return 6;
       g: [7, 8, 9]
      function clone(obj) {
       var target = {};
       for (var i in obj) {
        if (obj.hasOwnProperty(i)) {
         target[i] = obj[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

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);
JSON stringify/parse
var newObject = JSON.parse(JSON.stringify(oldObject));
var newObject = jQuery.extend({}, oldObject);
clone function
var newObject = clone(oldObject);
ES5 Object.clone
var newObject = Object.clone(oldObject);
var newObject = JSON.parse(JSON.stringify(oldObject));

Compare results of other browsers


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1 comment

Alexandre Paquette commented :

The "clone" method is not exactly a deep clone; It would have to test if the property value is also an object and call clone recursively, because otherwise you would still have a reference to the inital object instead of a copy (like the G property, pointing to an array)

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