Right, it existed before Angular 2, but Angular 2 put a lot of pressure over TypeScript and Microsoft to make it compatible with JavaScript. Before it, they had some incompatibilities with JavaScript, it was not technically a superset.

But nowadays it is. And a superset it means that TypeScript has some things that are not JavaScript. But everything that is JavaScript is TypeScript today.

You can rename any .js to .ts and it works.

I did that comment because often people forget about it, without knowing that choosing TS or JS is not as a hard decision as it seems. Even when you choosed TS, you can go back JS as fast as typing tsc.

Thanks for the clarification!