Cloning an Object

JavaScript performance comparison

Revision 19 of this test case created and last updated

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>
  function clone(obj) {
   var target = {}, i;
   for (i in obj) { if (obj.hasOwnProperty(i)) { target[i] = obj[i]; } }
   return target;
  }

function cloneDeeper(obj){
    if (obj === null || typeof obj !== 'object') { return obj; }

    var key, temp = new obj.constructor();
    for(key in obj) { temp[key] = clone(obj[key]); }

    return temp;
}
  
  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>
<script>
  Benchmark.prototype.setup = function() {
    var oldObject = {
       a: 1, b: 2, c: 3, d: 4, e: 5,
       f: { val: { val: { val: 6 } } },
       g: [7, 8, 9]
    };
  };

  Benchmark.prototype.teardown = function() {
    newObject.a = 10;
    if (oldObject.a === 10) {
      throw {message: "Test failed! Not a deep clone"};
    }
    if (!newObject.hasOwnProperty('b')) {
      throw {message: "Test failed! Not a deep clone (hasOwnProperty)"};
    }
    oldObject.f.val.val.val = 7;
    if (newObject.f.val.val.val === 7){
      throw {message: "Test failed! Not a deep clone"};
    }
    if (newObject.g[0] !== 7){
      throw {message: "Test failed! Not a deep clone (array)"};
    }
  };
</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…
deeper clone function
 
var newObject = cloneDeeper(oldObject);
 pending…
ES5 Object.create
 
var newObject = Object.create({}, oldObject);
 pending…
__proto__
 
var newObject = {__proto__:oldObject};
 pending…

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