When extending javascript functionality, what is the difference between Number and Math function?

I have extended javascripts core functionality by creating a few functions that were useful to me. When creating test cases for a function today I started wondering which way is the best to extend javascripts functionality for integer numbers. Using Number.prototype, or the Math object.

Number.prototype.sqr = function () {
    return this * this;
};
var test1 = (6).sqr();
alert("This is 36: " + test1);

OR

Math.sqr = function (num) {
    return num * num;
};
var test2 = Math.sqr(6);
alert("This is 36开发者_如何学编程: " + test2);

These two examples could be switched around for any integer type function that you would like to create, so which should be used?

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I 'd go with Math.sqr, because it doesn't force the reader of the code to think "what is this thing that has an sqr member?". Of course in a real program you wouldn't see (6).sqr() which might make it clearer what is going on, but rather some variable.

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Doesn't really matter, whatever syntax you prefer. That's not case when you start messing with Array.prototype or (GASP) Object.prototype.

Simply for consistency, I prefer to modify Math since other things like pow, sqrt, sin, etc are in there.