I'm glad you asked. :-) For a start, number types. I want i32, i64, u32 etc. JavaScript (and therefore TypeScript) only has "number". Yes we now finally have BigInt but it's not ideal for JIT optimisation.
Object prototypes is a weird part of JS that we really could do without. If you really want that, use class syntax.
The Date object. Need I say more...
Little things like Object.keys() should return a (keyof T)[] rather than a string[] but can't due to JS edge cases.
Want first class tuples/immutable arrays.
Many other new syntaxes that can't be implemented due to the need for JS compatibility.
I'm sure there are others that I can't think of right now...
Object prototypes is a weird part of JS that we really could do without. If you really want that, use class syntax.
The Date object. Need I say more...
Little things like Object.keys() should return a (keyof T)[] rather than a string[] but can't due to JS edge cases.
Want first class tuples/immutable arrays.
Many other new syntaxes that can't be implemented due to the need for JS compatibility.
I'm sure there are others that I can't think of right now...