Cloning an Object

JavaScript performance comparison

Revision 79 of this test case created by Marcin

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>
/*
   Description: Performs JSON-safe deep cloning. Equivalent of JSON.parse(JSON.stringify()).
   Based on deepClone7() by Kyle Simpson (https://github.com/getify)
   Source: http://jsperf.com/deep-cloning-of-objects,
   http://jsperf.com/structured-clone-objects/2
   https://developer.mozilla.org/en-US/docs/Web/Guide/DOM/The_structured_clone_algorithm
   */


  function deepCopy(objToBeCopied) {
    if (objToBeCopied === null || !(objToBeCopied instanceof Object)) {
      return objToBeCopied;
    }
    var copiedObj, fConstr = objToBeCopied.constructor;
    copiedObj = new fConstr();
    for (var sProp in objToBeCopied) {
      if (objToBeCopied.hasOwnProperty(sProp)) {
        copiedObj[sProp] = deepCopy(objToBeCopied[sProp]);
      }
    }
    return copiedObj;
  }

  var oldObject = {
   a: 1,
   b: 2,
   c: 3,
   d: 4,
   e: 5,
   f: {foo: "Bar", baz: "BART"},
   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) {
    return Object.keys(obj).reduce(function(c,k){c[k]=obj[k];return c;},{})
  }
 
  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…
clone2
var newObject = clone2(oldObject);
pending…
deepCopy
var newObject = deepCopy(oldObject);
pending…

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