how to define type of getter in typescript code example

Example 1: typescript get type

if (typeof abc === "number") {
    // do something
}

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