Javascript deep copying object [duplicate]

Question

Possible Duplicate:
What is the most efficient way to clone a JavaScript object?

I have an object like this:

User = {    
  name: "user",
  settings: {
    first: "1",
    second: "2"    
  }    
}

and a second one:

user1 = {
  name: "user1",
  settings: {
    second: "3"
  }
}

now I want to copy user1's custom values into User, using:

    for(var key in user1){
        User[key] = user1[key];
    }

the result User will be:

User = {
  name: "user1",
  settings: {
    second: "3"
  }
}

User.settings has been entirely replace while I wanted only settings.second to be replaced.

How to achieve this, without knowing how much child object the main object have?

Use recursion? Have you searched for deep Object.copy functions? — Bergi
– Bergi, Commented Jul 2, 2012 at 18:42
Because of how javascript passes objects around (by reference), deep copying a nested object is actually quite an ordeal. I'd follow @Bergi's advice and find a pre-existing one. — Mike Robinson
– Mike Robinson, Commented Jul 2, 2012 at 18:55
"This question has been asked before and already has an answer." So I ask to the moderators, where? Where has it been asked before? Why do you put the burden on the user to dig around and find it? — Dave Jensen
– Dave Jensen, Commented May 15, 2014 at 21:29

Matteo Pagliazzi · Accepted Answer · 2012-07-03 14:30:00Z

17

I've found that the best way to go is this:

http://andrewdupont.net/2009/08/28/deep-extending-objects-in-javascript/

Object.deepExtend = function(destination, source) {
  for (var property in source) {
    if (typeof source[property] === "object" &&
     source[property] !== null ) {
      destination[property] = destination[property] || {};
      arguments.callee(destination[property], source[property]);
    } else {
      destination[property] = source[property];
    }
  }
  return destination;
};


Object.extend(destination, source);

What about this?

    function clone(destination, source) {
        for (var property in source) {
            if (typeof source[property] === "object" && source[property] !== null && destination[property]) { 
                clone(destination[property], source[property]);
            } else {
                destination[property] = source[property];
            }
        }
    };

edited Jul 3, 2012 at 14:30

answered Jul 3, 2012 at 12:45

Matteo Pagliazzi

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6 Comments

Bergi Over a year ago

arguments.callee is deprecated. You should really use a named function. Also, you forgot about hasOwnProperty which is quite essential.

Bergi Over a year ago

Yes, although you still copy properties from the prototype. And copying to a destination object really should be called "extend", not "clone" (the "deepextend" from your first try would be even better)

Jon Jaques Over a year ago

My solution accounts for all of this ;) A plus one would be nice, atleast.

Eliran Malka Over a year ago

what about arrays (with nested objects)?

yazjisuhail Over a year ago

how about this implementation?

|

Jon Jaques · Accepted Answer · 2014-01-02 21:40:48Z

5

Grabbed jQuery's extend method, and made it library agnostic.

Gist: Library agnostic version of jQuery's Extend

Its wrapped in an Extender constructor, so you don't have to instantiate all of its internal methods each time you call the extend method.

Disclaimer: I have not tested this extensively. It's basically a 1:1 clone of jQuery's extend(), however your mileage may vary.

Use it like this.

var user1 = {
  name: "user1",
  settings: {
    first: "1",
      second: {bar: 'foo'}
  }
};
var user2 = {
  name: "user2",
  settings: {
    second: {foo:'bar'}
  }
};

/* merge user1 into User */
__extend(true, user1, user2);

// Modifies the User object
user1.settings.second.foo == 'bar'; // true

// note, you can do assignment too.
var newUser = __extend(true, user1, user2);

See here for more documentation

edited Jan 2, 2014 at 21:40

answered Jul 3, 2012 at 0:41

Jon Jaques

4,4202 gold badges25 silver badges25 bronze badges

2 Comments

Somojojojo Over a year ago

This might be lengthier than other solutions but it works reliably, and works on both array and object types. Thank you!

Simon Katan Over a year ago

This helped me in rhino .. cheers

Phillip Whisenhunt · Accepted Answer · 2012-07-02 19:20:00Z

-1

This is really hacky, but this should work. I suggest doing as the other users have suggested in the comments; find a pre-existing library that will do this for you.

for(var key in user1){  
   var temp = User[key]
   User[key] = user1[key];   
   for(var key1 in temp){
      if(User[key][key1] == null){
         User[key][key1] = temp[key1];
      }
   }
}

answered Jul 2, 2012 at 19:20

Phillip Whisenhunt

1,3152 gold badges18 silver badges30 bronze badges

4 Comments

Matteo Pagliazzi Over a year ago

the object i posted was an example i'm in search of something that will work everywhere

Phillip Whisenhunt Over a year ago

O ok. Well I would take a look at jQuerys api.jquery.com/jQuery.extend, it looks like it may do exactly what your looking for.

Matteo Pagliazzi Over a year ago

i've found this which seems to be working (not perfect but a start) my.opera.com/GreyWyvern/blog/show.dml/1725165, for jquery I'd like to kkep it framework agnostic

Mikko Ohtamaa Over a year ago

Be aware that this is very simple approach and you may run into some limitations - described here stackoverflow.com/questions/8092548/…

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