TypeScript 4.5.0 has issues with our MJS

[FossPrime]

Related to #1513

When using Node in ESM mode and TypeScript 4.5 with compilerOptions.module set to "node12" OR "nodenext" ESModuleInteropt is no longer needed and the MJS export can be used directly with TypeScript.

The problem comes when we use @types/koa... which doesn't define a default type export! Therefore Koa effectively has no types in this situation.

Solution #1

Make a named export called Application in the MJS wrapper.

Solution #2

Add types to the MJS export with dist/koa.d.ts that references the DefinitelyTyped Koa definitions

// dist/koa.d.ts
import { Application } from "@types/koa"
declare module "koa" {
  export const mod: Application
}

Solution #3

Rename mod to Application in dist/koa.mjs... then export Application as default

Details

• sandbox: run tsc in terminal
  • Check the Terminal not the IDE... TypeScript 4.5 is installed in the project but the sandbox IDE has an out of date TS version
• https://unpkg.com/browse/@types/koa@2.13.4/index.d.ts
• https://unpkg.com/browse/koa@2.13.3/lib/application.js

[killagu]

@rayfoss With this solutions, Should we use like import { Application} from 'koa'?

[FossPrime]

Lots of changes happened to ts-node, typescript... and even Node LTS. I can no longer reproduce.