Cloning an Object

JavaScript performance comparison

Revision 96 of this test case created

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="http://code.jquery.com/jquery-1.5.1.js" type="text/javascript"></script>


<script>
  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 clone2(obj) {
   var target = {};
   var keys = Object.keys(obj);
   for (var i = 0, len = keys.length; i < len; i++) {
     target[keys[i]] = obj[keys[i]];
   }
   return target;
  }
 
  function clone3(obj) {
   var target = {};
   for (var key in obj) {
     target[key] = obj[key];
   }
   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
   }
  });

  function cloneStupid(obj) {
      var target = [ obj ];
      return target.slice(0);
  }
</script>
<script>
Benchmark.prototype.teardown = function() {
    newObject.a = -911;
    console.log(oldObject);
    console.log("new:");
    console.log(newObject);
};
</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 = clone2(oldObject);
pending…
simple clone function
var newObject = clone(oldObject);
pending…
ES5 Object.clone
var newObject = clone3(oldObject);
pending…
Stupid Clone
var newObject = cloneStupid(oldObject);
pending…

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