Typescript augmentation

Question

I've been trying unsuccessfully to augment a type in agGrid with a few new properties.

import * as agGrid from 'ag-grid/main';

declare module "ag-grid/main" {
   export interface ColDef {
       format: string;
       unitType: string;
   }
}

Everything I have tried results in the original ColDef being overwritten and a build error of: Export declaration conflicts with exported declaration of 'ColDef'

Answer 1

So I figured out how to do this. The problem is you cannot augment a re-exported module. You have to directly import it.

import ColDef from 'ag-grid/dist/lib/entities/colDef';
// This is a patch to the ColDef interface which allows us to add new properties to it.
declare module "ag-grid/dist/lib/entities/colDef" {
    interface ColDef {
        format?: string;
        unitType?: string;
    }
}

This will apply to any library that re-exports it's modules. In the case of agGrid there is a main.d.ts which exports its modules from other definition files which export their modules directly.

More info here. https://github.com/Microsoft/TypeScript/issues/8427