A debounce function with type safety

debounce.ts

export const MissingReturnValue = Symbol('MissingReturnValue')

export function debounce<Fn extends (...args: any[]) => any>(
  fn: Fn,
  ms: number
): (...args: Parameters<Fn>) => ReturnType<Fn> | typeof MissingReturnValue {
  let debouncing = false
  let lastReturnedValue:
    | typeof MissingReturnValue
    | ReturnType<Fn> = MissingReturnValue
  let timeoutID: number

  return function debounced(
    ...args: Parameters<Fn>
  ): ReturnType<Fn> | typeof MissingReturnValue {
    if (debouncing === false) {
      debouncing = true
    } else {
      clearTimeout(timeoutID)
    }
    timeoutID = setTimeout(() => {
      debouncing = false
      lastReturnedValue = fn.apply(fn, args)
    }, ms)

    return lastReturnedValue
  }
}