Extend the number class

Question

I want to extend the number class to have instance functions such as odd and even so I can do something like this:

2.odd() => false
         


        

Answer 1

I think as long as you understand the side-effects of your "extension" then you're okay. I often modify the String prototype to add an "elipsis" method so I can do things like

"SomeString".elipsis()

But start at the beginning. You're not "extending classes" in JavaScript. JavaScript is a prototype-based language. You can modify prototypes to do what you need.

You won't be able to add a method directly to the number itself. You can, however modify the prototype of the Number object:

Number.prototype.even = function(){    
    return this.valueOf() % 2 === 0;
}

With this, you won't be able to use the following syntax:

10.even();

But, since you aren't hard-coding stuff, otherwise you wouldn't need this function anyways, you CAN do the following:

var a = 10;
a.even(); //true

I might say that you could consider adding a utilities object to do these things, because modifying primitive prototypes is not always guaranteed to be side-effect free.

This function does not really provide any gain for you. You're checking for odd and even, replacing one line of code with another. Think about the difference:

var a = 10;
var aIsEven = a.even();

vs:

var a = 10;
var aIsEven = a % 2 === 0;

You gain three characters of code, and the second option is less likely to break your "JavaScript".