This might be the most difficult process in TypeScript. If the module doesn't already contain type definitions, someone probably wrote them in the DefinitelyTyped repository (the types for my-module might be available if you npm install @types/my-module).

If you still run into errors with importing afterwards (or if a DefinitelyTyped module doesn't exist), add the following line to your index.d.ts:

declare module "my-other-module";

If necessary, restart the hot reloading process (ctrl-c and then npm start again).

Instead of using import myModule from "my-module, try import * as myModule from "my-module".

If you get a TypeScript compilation error after adding a new file and you have no idea why, restarting the hot reloading process usually works.