Debounce a function (Typescript)

debounce.ts

type Fn = (...args: any[]) => any;
type Callback<F extends Fn> = F extends Fn
  ? (...args: Parameters<F>) => ReturnType<F>
  : never;

function debounce<T extends Fn, O extends Callback<T>>(
  func: O,
  wait: number,
  immediate?: boolean
): O {
  let timeout: NodeJS.Timeout, result: ReturnType<O>;

  return function (...args) {
    clearTimeout(timeout);
    timeout = setTimeout(() => {
      timeout = null;
      if (!immediate) {
        result = func.call(this, ...args);
      }
    }, wait);

    if (immediate && !timeout) {
      result = func.call(this, ...args);
    }
    return result;
  } as O;
}