Javascript fastest way to duplicate an Array - slice vs for loop

Question

In order to duplicate an Array in Javascript,

does anyone know (and maybe tested) if it's faster to use slice method:

var dup_array = original_array.slice();

or doing a for loop:

for(var i = 0, l = original_array.lenght; i < l; ++i)
   dup_array[i] = original_array[i];

---

UPDATE: (just to clarify myself) I know both ways do only a shallow copy: if original_array contains references to objects, objects won't be cloned, but only the references will be copied therefor both arrays will have refrences to the same objects. But this is not the point of this question.

I'm asking only about speed.

Answer 1

Take a look at: link. It's not about speed, but comfort. Besides as you can see you can only use slice(0) on primitive types.

To make an independent copy of an array rather than a copy of the refence to it, you can use the array slice method.

Example:

To make an independent copy of an array rather than a copy of the refence to it, you can use the array slice method.

var oldArray = ["mip", "map", "mop"];
var newArray = oldArray.slice();

To copy or clone an object :

function cloneObject(source) {
    for (i in source) {
        if (typeof source[i] == 'source') {
            this[i] = new cloneObject(source[i]);
        }
        else{
            this[i] = source[i];
  }
    }
}

var obj1= {bla:'blabla',foo:'foofoo',etc:'etc'};
var obj2= new cloneObject(obj1);

Source: link

Answer 2

It depends on broswer, if you look at the link below there is a rough guide to performance of each: http://weblogs.asp.net/alexeigorkov/archive/2008/02/18/array-prototype-slice-vs-manual-array-creation.aspx

Answer 3

I put together a quick demo. http://jsbin.com/agugo3/edit

my results on IE8 are 156/782/750, which would indicate slice is much faster in this case.