cloning an object vs. 'new Fn()'

JavaScript performance comparison

Revision 57 of this test case created by Joe


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: "cat",
       d: "dog",
       e: 5,
       g: [0, 0, 0]
    var oldObjectFn = function() {
       this.a = 1;
       this.b = 2;
       this.c = "cat";
       this.d = "dog";
       this.e = 5;
       this.g = [0, 0, 0];
      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);
stringify eval
var newObject = eval("("+JSON.stringify(oldObject)+")");
Object.create() - NOTE: doesn't copy non-primitives
var newObject = Object.create(oldObject);
//this doesn't work when oldObject conatins non-primitive like arrays and other objects - instead it copies a reference to the object, which is not wanted in most cases.
new Fn()
var newObject = new oldObjectFn();

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