Typescript: Extend external modules declared in @types npm dependency

[nicojs]

TypeScript Version: nightly (2.0.0-dev.201xxxxx)

Code

npm i @types/estree;

// myESTreeExtension.ts
declare module 'estree' {
    interface MyAddon {
   }
}

// Some other file.ts
import * as estree from 'estree';

let a: estree.Node; // ERROR: [ts] Module ''estree'' has no exported member 'Node'.

Expected behavior:

I would expect i can extend an external module as described here: #280

Actual behavior:

The ambient module in myESTreeExtension.ts _overrides_ the @types/estree types

Remark: I'm a big fan of the new work flow with @types. Great job!

[mhegazy]

make sure the file that contains the module augmentation is itself a module (i.e. includes at least one top-level import or export).

so this should work:

import * as estree from 'estree';

declare module 'estree' {
    interface MyAddon {
   }
}

[nicojs]

Thanks @mhegazy, this works. When using the extensions you need to do this:

import * as estree from 'estree';
import 'myESTreeExtension';

let a: estree.Node; // Works
let b: estree.MyAddon; // Works as well

[Volox]

Sorry to ask here since the bug is closed but i have a similar problem with KoaJS definitions here.

The Koa definition file looks like this:

declare namespace Koa { }
export = Koa;
declare namespace Koa {
    export interface Context extends Request, Response {
    }
    // ... more things
}
declare class Koa extends EventEmitter {
   // ... things
}

And i want to be able to do something like (as suggested here and here):

import * as Koa from 'koa';
const server: Koa = new Koa();
server.name = 'UrbanScope';
server.context.db = db; // server.context is Koa.Context

But i keep getting TS2339 errors from tsc like:

src/server.ts(60,10): error TS2339: Property 'name' does not exist on type 'Koa'.
src/server.ts(63,18): error TS2339: Property 'db' does not exist on type 'Context'.

---

Following your advice i created a augment.ts file with:

import * as Koa from 'koa';
import { Db } from 'mongodb';
declare module 'koa' {
    namespace Koa {
        interface Context {
            db: Db,
        }
    }
    class Koa {
        name?: string;
    }
}

But the errors are still there 😨 , i tried with a number of export/namespace/class/declare combinations with no luck. Any idea on how to solve it?

[mhegazy]

given the way Koa is authored extending the class is not possible. as for the interface context, you should be able to do that as:

import * as Koa from 'koa';
import { Db } from 'mongodb';

declare module 'koa' {
        interface Context {
            db: Db,
        }
}

[Volox]

It works!
Thanks for you support!

[ivanpadavan]

And what should I do if package name starts with @?

[trusktr]

I'm trying to extend a class, but it seems to override the whole class with my new definition. F.e.:

import * as THREE from 'three' // includes a definition for OrbitControls

declare module 'three' {
    export class OrbitControls {
        setCamera( cam: THREE.Camera ): void
    }
}

Now my code has no errors when using the setCamera method, but there is now a type error on the use of all the other stuff in the OrbitControls class, so it looks like the @types/three version was replaced with my version.

How do we extend the class defintion of a module?

[milewski]

@trusktr r i believe you should do this instead

import * as THREE from 'three' // includes a definition for OrbitControls

declare module 'three' {
    export interface OrbitControls {
        setCamera( cam: THREE.Camera ): void
    }
}