Cloning an Object

JavaScript performance comparison

Revision 102 of this test case created by Alex

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;
  }
 
  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 cloneOURS(src) {
    function mixin(dest, source, copyFunc) {
        var name, s, i, empty = {};
        for (name in source){
            // the (!(name in empty) || empty[name] !== s) condition avoids copying properties in "source"
            // inherited from Object.prototype.   For example, if dest has a custom toString() method,
            // don't overwrite it with the toString() method that source inherited from Object.prototype
            s = source[name];
            if (!(name in dest) || (dest[name] !== s && (!(name in empty) || empty[name] !== s))) {
                dest[name] = copyFunc ? copyFunc(s) : s;
            }
        }
        return dest;
    }
    if (!src || typeof src != "object" || Object.prototype.toString.call(src) === "[object Function]") {
        // null, undefined, any non-object, or function
        return src;  // anything
    }
    if (src.nodeType && "cloneNode" in src) {
        // DOM Node
        return src.cloneNode(true); // Node
    }
    if (src instanceof Date) {
        // Date
        return new Date(src.getTime());  // Date
    }
    if (src instanceof RegExp) {
        // RegExp
        return new RegExp(src);   // RegExp
    }
    var r, i, l;
    if (src instanceof Array) {
        // array
        r = [];
        for (i = 0, l = src.length; i < l; ++i){
            if (i in src){
                r.push(clone(src[i]));
            }
        }
    } else {
        // generic objects
        r = src.constructor ? new src.constructor() : {};
    }
    return mixin(r, src, clone);
};

function deepCloneX( object ) {
      if( !object || typeof( object ) !== 'object' ) {
         return object;
      }

      var result;
      if( type( object ) === 'array' ) {
         result = [];
         for( var i = 0, length = object.length; i < length; ++i ) {
            result[ i ] = deepCloneX( object[ i ] );
         }
      }
      else {
         result = {};
         for( var key in object ) {
            if( object.hasOwnProperty( key ) )  {
               result[ key ] = deepCloneX( object[ key ] );
            }
         }
      }

      return result;
   }

function type( object ) {
      if( object === null ) {
         return 'null';
      }
      if( typeof object === 'undefined' ) {
         return 'undefined';
      }

      var tmp = Object.prototype.toString.call( object ).split( ' ' )[1];
      if( !tmp ) {
         return undefined;
      }
      return tmp.substr( 0, tmp.length - 1 ).toLowerCase();
   }
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;
}
</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…
cloneOURS
var newObject = cloneOURS(oldObject);
pending…
deepCloneX
var newObject = deepCloneX(oldObject);
pending…
cloneDeeper
var newObject = cloneDeeper(oldObject);
pending…

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Revisions

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