what is a type argument in typescript code example

Example 1: typescript function type

interface Date {
  toString(): string;
  setTime(time: number): number;
  // ...
}

Example 2: get function return type typescript

type return_type = ReturnType<() => string>; // string
// or
function hello_world(): string {
  return "hello world";
}
type return_type = ReturnType<typeof hello_world>; // string