Apart from the obvious type system, I have read that there are features in TypeScript that are not available in ES6. The article did not mention what these features were or why they should be avoided.
I am already aware that TypeScript implements ES7 async/await syntax and this post (Which ES6 Features are Implemented in Typescript) gives us the inverse relationship.
New features that do not exist in ES 6
As @A Red Herring says:
That is why don't forget about pure JS features, and thinking in JS, but not in TypeScript