I like TypeScript's syntax, but I think the way function types are declared is ugly.

If you have a function from A to B, you have to declare its type as

    type MyFunction = (arg1: A) => B

instead of

    type MyFunction = A => B

Here's that syntax applied to the example from GP:

    function call<TS extends any[], R>(fn: (...args: TS) => R, ...args: TS): R { return fn(...args); }

vs.

    function call<TS extends any[], R>(fn: ...TS => R, ...args: TS): R { return fn(...args); }