Merge interface from namespace in module declaration file

Question

I have a javascript library which has a type definition file here: https://github.com/tyranid-org/tyranid/blob/master/tyranid.d.ts which is exposed via the typings

Answer 1

You're trying to augment the module tyranid. The general syntax is pretty straightforward: here is an example of redux-thunk augmenting redux.

However, because tyranid exports default, module augmentation is not fully supported. export = has been fixed, as discussed in this issue.

To augment tyranid, the best I could come up with (inspired by this comment), is to throw the Tyr namespace into the global scope:

node_modules/tyranid/tyranid.d.ts

import * as Express from 'express';
import * as mongodb from 'mongodb';

export default TyrStatic;

declare global {
  namespace TyrStatic {
    // existing implementation of the Tyr namespace
  }
} 

./index.d.ts

declare namespace TyrStatic {
  interface specialInterface {
    someProp: number
  }
}

(depending on whether you need this augmentation to use external modules, you might need to wrap it in a declare global {})

src/app.ts

import Tyr from 'tyranid'
let specialVariable: Tyr.specialInterface = { someProp: 4 }

Answer 2

The following ended up working...

in node_modules/tyranid/tyranid.d.ts:

export = Tyr // must do "import * as Tyr from 'tyranid'" instead of default

declare namespace Tyr {
  export interface Document {
    // original definition...
  }
}

in mylib/tyranid-extensions.d.ts...

declare module "tyranid" {
  interface Document {
    addedMethod(): boolean; 
  }
}

Thanks @pelle-jacobs for the help!