[rellekio]

No: If (typeof x === 'string') {}

I personally love TypeScript, but I do have one big hang up. Janky builds in testing. Can't explain it, but sometimes the guarantees TS is supposed to provide don't compile over. Mainly while using nodemon or another auto compile. Have only ran into it a couple times, but it mainly crops up during module linking.

Also keep in mind you can use as modules via require('') and skip adding types to a js lib. Be sure to add --module commonjs or the equivalent in config.

Why I like TypeScript for myself is writing modules and api's. Mainly: inline documentation. And the pursuit of more of a deterministic outcome in your programs. Still the linking issue bothers me.