Extending Number.prototype in javascript and the Math object?

Question

I've always wondered why Javascript has the global Math object instead of giving numbers their own methods. Is there a good reason for it?

Also are there any drawbacks (other than efficiency) to doing something like this?:

Number.prototype.round = function(){
    return Math.round(this);
};

Just to make clear, I understand that constants like π need somewhere and functions that are applied on more than one number like min/max. The question was mainly concerning methods which only effect a single number such as round, abs, sin, pow, etc.

Answer 1

I think Math is more than set of Number methods. It's usage wider. Say, using NumberVariable.PI can be confusing. Same with random numbers generation.

Also I think extending number is OK, because it's the part of JS nature. Maybe someone will correct me if I am wrong here.

Answer 2

There is no drawback in extending Number.prototype other then confusing other people. What's the point? What is better in using value.round() instead of Math.round(value)?

There are several good reasons for the Math object:

1. It works for non-numbers, too: Math.round("5") works whereas value.round() won't work when value is a string (for example, the value of a textbox)
2. Some members of the Math object don't belong to a "primary" number value, like Math.min() or Math.max(). Or do you want to use it like a.max(b)?
3. Other members are global and do not belong to a specialized number. Examples are constants like Math.PI or the function Math.random().

Answer 3

The reason for the Math object is simple: "because Java does it". Not the best of reasons, but here we are. I guess things made more sense back then, before Douglas Crockford started his campaign to suppress half the language*. Originally you were "allowed", or ment, to do things like this:

with (Math) {
  var n = min( round(a) * round(b), sqrt(c) );
  var result = exp( n + d );
}

The drawback to extending Number.prototype is: What if someone else does the same thing? Or worse: What if someone else, who's library/script is included on the same page, decides that Number.prototype.round should be, say, a symmetrical rounding function?

If you are looking for ways to make your life easier, why stop there? Why not simply include Math functions as global funtions?

var m = 'abs acos asin atan atan2 ceil cos exp floor log max min ' +
        'pow random round sin sqrt tan PI').split(' ');
for (var i=0,l=m.length; i<l; i++) {
  window[ m[i] ] = Math[ m[i] ];
}

This will drop all the math functions into the global scope, effectively allowing you to stop typing "Math." Ask yourself: Is there any real difference between extending number and extending window with these functions?

* Before you flame me: The Crockford comment is not ment to be taken to seriously. I do agree with him that with is very dangerous in an implicit global environment.

Answer 4

Try doing 123.round();

Your javascript console will throw a few hundred of errors to your eyes :P, nah ...

You can do:

Number.prototype.x then: (123).x(); but never 123.x();