How to extend a primitive type in typescript?

Question

I want to create an interface like this:

interface Show { show(): string; } function doit(s: Show) { return 'Showed: ' + s.show(); }

Then we can use it with a new class:

 class Foo { s: string; constructor(s: string) { this.s = s; } show() { return 'Foo with "' + this.s + '"'; } } console.log(doit(new Foo('hello')));

I would like to do the same for Number s. In simple JavaScript, I could make the Number type, for example, execute this interface with:

 Number.prototype.show = function() { return '' + this; }

But TypeScript does not allow me to do this:

 show.ts(18,18): error TS2094: The property 'show' does not exist on value of type 'Number'.

Is there any way to do this?

+2

javascript interface typescript

limp_chimp Apr 26 '14 at 4:15

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1 answer

basarat · Answer 1 · 2014-04-26 05:02

Just tell TypeScript about this by adding to Number :

 interface Number{ show():string; } Number.prototype.show = function() { return '' + this; } var foo = 123; foo.show();