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, Dec 21 '11 at 18:15

score 2 · Accepted Answer · answered Dec 21 '11 at 18:15

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 '11 at 18:15

Adam Rackis · Answer 2 · 2011-12-21T18:35:13.700

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 '11 at 18:35

answered Dec 21 '11 at 18:15

Adam Rackis

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+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; }` – Dec 21 '11 at 23:04

score 1 · Answer 3 · answered Dec 21 '11 at 18:22

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);

score 0 · Answer 4 · answered Dec 21 '11 at 18:17

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 '11 at 18:17

zzzzBov

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cloning an object in Javascript maintaining instanceof

4 Answers4