In JavaScript, is there a way to inherit from the Number function?

So I know I can do this...

Number.prototype.square = function () { return this * this }

Is there a way to inherit from the Number function so that I don't have to modify the Number prototype? With a function or object, I can inherit like this...

var NewObject = new Object()
var NewFunction = new Function()

Is there a was to do something similar w/ Number?



Yes, you can easily inherit from the Number.prototype. The trick is to make your objects convertible to numbers by giving them a .valueOf method:

function NumLib(n) {
    if (!(this instanceof NumLib)) return new NumLib(n);
    this.valueOf = function() {
        return n;
NumLib.prototype = Object.create(Number.prototype);
NumLib.prototype.square = function () { return this * this }

The cast will happen whenever a mathematical operation is applied to the object, see also this answer. The native Number methods don't really like to be called on derived objects, though.


using Object.defineProperty allows you to have a little more control over the object.

 return this*this

with your own lib it's the same...

 return this.whatever*this.whatever


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