Cloning an Object

JavaScript performance comparison

Revision 40 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]
  };
  var i = 1000;
  while (i--)
    oldObject[Math.random()] = i;
  
  function clone(obj) {
   var target = {};
   for (var i in obj) {
    if (obj.hasOwnProperty(i)) {
     target[i] = obj[i];
    }
   }
   return target;
  }
var extend = function(source, target) {
    var keys = Object.keys(source),
        i = keys.length,
        target = target || {};
    while (i--) {
        target[keys[i]] = source[keys[i]];
    }
    return target;
}
    var fork = function(source) {
        var
        objmap = new Map(),
        targetOut = {__proto__: source.__proto__},
        target,
        stack = {0: {source: source, target: targetOut}},
        sp = 0,
        ss = 1,
        keys, key, j, scope, tmp;
        while ((scope = stack[sp++])) {
            keys = Object.keys(scope.source);
            j = keys.length;
            while (j--) {
                source = scope.source[key = keys[j]];
                if (source !== null && source === Object(source)) {
                    if ((tmp = objmap.get(source))) {
                        scope.target[key] = tmp;
                    } else {
                        scope.target[key] = target = {__proto__: source.__proto__};
                        stack[ss++] = {source: source, target: target};
                        objmap.set(source, target);
                    }
                } else {
                    scope.target[key] = source;
                }
            }
            delete stack[sp - 1];
        }

        target = source = stack = keys = key = scope = null;
        return targetOut;
    };




  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…
efficient deep clone
 
var newObject = fork(oldObject);
 pending…
efficient extend
 
var newObject = extend(oldObject);
 pending…

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