Cloning an Object

JavaScript performance comparison

Revision 23 of this test case created by Jesper Petersson

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. (see Revision 3 by Corban Brook)

Revision 22: added LoDash since someone brought Underscore, using CDN for UnderScore

Preparation code

<script src="http://code.jquery.com/jquery-1.5.1.js" type="text/javascript"></script>
<script src="http://cdnjs.cloudflare.com/ajax/libs/underscore.js/1.3.3/underscore-min.js"></script>
<script>var underscore = _.noConflict();</script>
<script src="https://raw.github.com/bestiejs/lodash/master/lodash.min.js"></script>
<script>var lodash = _.noConflict();</script>
<script>
  //allow UnderScore vs LoDash
  var lodash = window.lodash,
      underscore = window.underscore;

  //continue test setup
  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;
  }

  function clone_deep(obj) {
    var target = {};
    for (var i in obj) {
      if (typeof(obj) === 'object') {
        target[i] = clone_deep(obj[i]);
      }
      else {
        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
    }
  });
</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…
slice(0)
var newObject = oldObject.slice(0);
pending…
underscore.clone
var newObject = underscore.clone(oldObject);
pending…
lodash.clone
var newObject = lodash.clone(oldObject);
pending…
clone_deep
var newObject = clone_deep(oldObject);
pending…

Compare results of other browsers

Revisions

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1 comment

Kyle Simpson commented :

Most of these that claim to do deep cloning don't actually do valid deep cloning. This is a typical case where this jsperf doesn't tell you anything useful since it test apples, oranges, and bananas against each other. OBVIOUSLY shallow clone (if acceptable) is faster than deep clone. This test SHOULD only do one or the other.

To fix that, I put up this jsperf, which tests ONLY deep clone (and shows where 2 of them fail):

http://jsperf.com/deep-cloning-of-objects

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