debounce

debounce.ts

export interface Debounced<F extends (...arg: any[]) => any> {
  (...args: Parameters<F>): void;

  clear(): void;
}

/**
 * Returns a function that executes `func` until after `wait`
 * milliseconds have elapsed since the last time the debounced function was
 * invoked.
 *
 * The debounced function provides a `clear` handle to cancel a pending execution.
 */
export function debounce<Func extends (...arg: any[]) => any>(
  func: Func,
  waitMs: number
): Debounced<Func> {
  if (typeof func != 'function') {
    throw new TypeError('debounce: input is not a function');
  }

  let timeoutRef: ReturnType<typeof setTimeout> | undefined;
  const clear = (): void => {
    if (timeoutRef) {
      clearTimeout(timeoutRef);
      timeoutRef = undefined;
    }
  };
  const output = function (this: unknown, ...args: Parameters<Func>) {
    clear();

    timeoutRef = setTimeout(() => {
      func.apply(this, args);
    }, waitMs);
  };

  (output as Debounced<Func>).clear = clear;

  return output as Debounced<Func>;
}