Array() and Array.prototype usage

Question

First of all i would like to ask for excuse if answer is obvious, and/or easy to find. I didn't find any complete answers.

The question is very simple:

var array1 = Array().slice.call(arguments,1);
var array2 = Array.prototype.slice.call(arguments,1);

They do the same thing. Can you do in such a way for Object, Date, String, etc prototypes

Answer 1

Yes you can, simply because each instance inherits from its constructor's prototype.

That is (new Array()).slice (or better, [].slice) is exactly the same method as Array.prototype.slice.

• user236139: It should be noted that while this works for Arrays because of the way the spec sets up behavior of Array (as a constructor) when called as a function, this does not necessarily extend to the other objects mentioned in the question. For example, if you do Date.prototype.test = 1; and then Date().test, you get nothing because of the way Date (as a constructor) acts as a function.
• Felix Kling: Yes, I was thinking about mentioning this, but I did not want to make it too confusing. It's enough to say that Date does not return a Date instance when called without the new keyword (it returns a string).
• user236139: Yeah, I think the constructor/function duality is probably more of the one confusing aspects of JavaScript.
• Felix Kling: For example? Number().toFixed.call(5.12, 1) is the same as Number.prototype.toFixed.call(5.12, 1)...
• Felix Kling: @Elmor: Ah well, that is something completely different. You cannot assign properties to primitive values.

Answer 2

The second approach is better, as you're not creating an Array that is otherwise unused. With the first approach, you're constructing an array, and then using dynamic prototype chain resolution to locate it's slice method, which you then call using your arguments as the context. The second approach directly access the slice method, so you're avoiding the object creation and prototype chain resolution, so it's all around better.