You can annotate your code with JSDoc comments and get the full value of TypeScript while just writing JavaScript without any transpilation step[1]. It won’t help you with IE11 support though.
That's a helpful feature but it's by no means a replacement for Typescript. You do not get the full value with just inline comments, in fact that usage is extremely limited.
1: https://www.typescriptlang.org/docs/handbook/intro-to-js-ts....