cloning an object in Javascript maintaining instanceof

Question

I want to clone an object in Javascript. I have:

 iPath = function () { this.heading = 0; this.path = []; };
 loop = new iPath();

I know with jQuery I can do something like:

 cloneLoop = $.extend(true, {}, loop);

but than

 assert(cloneLoop instanceof iPath, "fails because loop is not an iPath");

How can i do a deep clone fulfilling last assert statement?

"deep" extension means that sub-objects will be merged as well. extend does not clone an object, it does not preserve the prototype chain either. — zzzzBov
– zzzzBov, Commented Dec 21, 2011 at 18:15

user1106925 · Accepted Answer · 2011-12-21 18:15:43Z

2

How about this:

cloneLoop = $.extend(true, new iPath(), loop);

...though I'm not sure if you'd want to do a deep copy. I'd think this would be better:

cloneLoop = $.extend(new iPath(), loop);

answered Dec 21, 2011 at 18:15

user1106925

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Comments

Alex Wayne · Accepted Answer · 2011-12-21 18:22:31Z

1

Extend simply copies properties from one object to another. So you have to start with a pristine copy of the object you want to copy into. So use new iPath() instead of {}.

var iPath = function () { this.heading = 0; this.path = []; };
loop = new iPath();

cloneLoop = $.extend(true, new iPath(), loop);

alert(cloneLoop instanceof iPath);

answered Dec 21, 2011 at 18:22

Alex Wayne

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Comments

Adam Rackis · Accepted Answer · 2011-12-21 18:35:13Z

1

If not supporting older browsers is an option, you should be able to use Object.create:

var cloneLoop = Object.create(loop);

Here's a demo

    function Foo() {
        this.x = 1;
        this.y = 1;
        this.blah = { f: "a", g: "b" };
    }

    var f = new Foo();
    var clone = Object.create(f);

    alert(clone instanceof Foo);
    alert(clone.blah.f);

alerts true, then a (at least on Chrome, older browsers will not support Object.create)

edited Dec 21, 2011 at 18:35

answered Dec 21, 2011 at 18:15

Adam Rackis

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1 Comment

user1106925 Over a year ago

+1 Seems like setting it as the prototype object would be a good solution. For older browsers, you can use the typical Object.create patch. function create( proto ) { function f(){} f.prototype = proto; return new f; }

zzzzBov · Accepted Answer · 2011-12-21 18:17:37Z

0

You'll need to write your own clone method:

Something along the lines of:

iPath.prototype = {
  clone: function () {
    var p;
    p = new iPath();
    $.extend(true, p, this);
    return p;
  }
}
cloneLoop = loop.clone();

answered Dec 21, 2011 at 18:17

zzzzBov

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