Copy and extend global objects in javascript

Question

is there a way to copy a global object (Array,String...) and then extend the prototype of the copy without affecting the original one? I've tried with this:

var copy=Array;
copy.prototype.test=2;

But if i check Array.prototype.test it's 2 because the Array object is passed by reference. I want to know if there's a way to make the "copy" variable behave like an array but that can be extended without affecting the original Array object.

Answer 1

Good question. I have a feeling you might have to write a wrapper class for this. What you're essentially doing with copy.prototype.test=2 is setting a class prototype which will (of course) be visible for all instances of that class.

Answer 2

I think the reason the example in http://dean.edwards.name/weblog/2006/11/hooray/ doesn't work is because it's an anonymous function. So, instead of the following:

// create the constructor
var Array2 = function() {
  // initialise the array
};

// inherit from Array
Array2.prototype = new Array;

// add some sugar
Array2.prototype.each = function(iterator) {
// iterate
};

you would want something like this:

function Array2() {

}
Array2.prototype = new Array();

From my own testing, the length property is maintained in IE with this inheritance. Also, anything added to MyArray.prototype does not appear to be added to Array.prototype . Hope this helps.

Answer 3

Instead of extending the prototype, why don't you simply extend the copy variable. For example, adding a function

copy.newFunction = function(pParam1) { 
      alert(pParam1);
};