Extending instance/static functions on existing prototypes with TypeScript

Question

I recently asked a question about TypeScript's ability to extend existing prototypes in the JavaScript API (here: Extending Object.prototype with TypeScript).

This turned out to be a bug, which has since been resolved as of TypeScript 0.9.0 Alpha (which now includes generics...GREAT :-))

In TypeScript, interfaces are open ended, so if you look in lib.d.ts, you will find an interface which defines the contract for JavaScript's Object API. You should also see a variable declaration for Object, which defines Object's static functions.

For the sake of simplicity, here they are:

//Pulled from lib.d.ts

interface Object {
    toString(): string;
    toLocaleString(): string;
    valueOf(): Object;
    hasOwnProperty(v: string): bool;
    isPrototypeOf(v: Object): bool;
    propertyIsEnumerable(v: string): bool;
    [s: string]: any;
}

declare var Object: {
    new (value?: any): Object;
    (): any;
    (value: any): any;
    prototype: Object;
    getPrototypeOf(o: any): any;
    getOwnPropertyDescriptor(o: any, p: string): PropertyDescriptor;
    getOwnPropertyNames(o: any): string[];
    create(o: any, properties?: PropertyDescriptorMap): any;
    defineProperty(o: any, p: string, attributes: PropertyDescriptor): any;
    defineProperties(o: any, properties: PropertyDescriptorMap): any;
    seal(o: any): any;
    freeze(o: any): any;
    preventExtensions(o: any): any;
    isSealed(o: any): bool;
    isFrozen(o: any): bool;
    isExtensible(o: any): bool;
    keys(o: any): string[];
}

So, my previous question was about extending the interface for Object, like so:

interface Object {
    GetFoo(): Foo;
}

Object.prototype.GetFoo = function() {
    return new Foo();
}

As stated, this works as of TypeScript 0.9.0.

But now I also want to be able to add static functions to Object, perfectly legal in pure JavaScript.

In JavaScript I would do:

Object.FooAgain = function () {
    // Yes, it's foo again!
}

But I can't seem to be able to accomplish this in TypeScript.

First I tried to see if Object's declaration was open ended (as with interfaces):

declare var Object: {
    FooAgain(): void;
}

Object.FooAgain = function () {
    // TS doesn't like this, and Object.FooAgain isn't available in intellisense.
}

I also tried (I saw this in another article, and thought it was worth a try).

export declare var Object: {
}

but this seems to break everything even more...

Admittedly this issue may have also been fixed in TS 0.9.0 (I'm at work so I haven't actually tried it fully).

Can anyone shed some light on this?

Answer 1

Since TypeScript 1.4 static extensions can be added easily. The TypeScript team changed the lib.d.ts file to use interfaces for all static type definitions.

The static type definitions are all named like [Type]Constructor: So if you want to add a static function to type Object, then add your definition to ObjectConstructor.

Definition:

interface ObjectConstructor
{
    FooAgain(): void;
}

Implementation:

Object.FooAgain = function(): void
{
    // Oh noes, it's foo again!
}