Call a member of an object with arguments

I think this does the trick:

function callMethodWithArgs<
  M extends keyof T,
  T extends { [m in M]: (...args: Array<any>) => any },
  F extends T[M]
>(obj: T, methodName: M, args: Parameters<F>) {
  return obj[methodName](...args) as ReturnType<F>;
}

Requires TS 3 though!