The greater community can write their own type definitions (.d.ts files) for non-TypeScript packages – which is pretty much every popular library on NPM
To help understand how we, as a community, got here and where we’re going next I’m going to give you a quick history lesson.
Welcome to the past, the wild west of .d.ts files. A community project called DefinitelyTyped, started by Boris Yankov, is first committed to over three years ago. DefinitelyTyped has evolved 100 times over since the initial inception, but the core premise is to use ambient module declarations that define types for packages in NPM, Bower and the browser.