[pingec]

My experience: I ported a 12k LOC app from javascript to typescript. It spotted about 5 typos where I was checking for a misspelled prop which always evaluated to false. Also I prefer how more clean classes look in typescript than in js but when compiled the js code is as I would have written it manually.

Also, I love the intellisense provided by VS through type definitions which also means less time spent on checking API docs, so far I've had very few problems with wrong or lacking type definitions for libs.

But it's not all about types. From what I've read from TS devs, they are trying to implement all ECMAScript 6 in TS so that basically (among other things) it gives you the javascript of tomorrow, today.