throttle.js

/**
 * throttle
 *
 * @since 1.3.0
 * @author caiyue;
 * @param func {function}
 * @param wait {number}
 *
 * @example
 *
 * var debounced = throttle(()=>{console.log(123)}, 500);
 * //cancel the throttle function
 * debounced.cancel();
 */

const throttle = (func, wait) => {
  if (typeof func !== 'function') {
    throw new TypeError('Expected a function');
  }
  let timerId;
  let startTime = 0;

  function cancel() {
    clearTimeout(timerId);
    //reset countdown
    startTime = 0;
  }

  function debounced() {
    let now = Date.now();
    // start countdown
    if (!startTime) {
      startTime = now;
    }
    // countdown over
    if (now - startTime >= wait) {
      func();
      // reset countdown
      startTime = 0;
      return;
    }    
    clearTimeout(timerId);
    timerId = setTimeout(() => {
      func();
      // reset countdown
      startTime = 0;
    }, wait);
  }

  debounced.cancel = cancel;
  return debounced;
};
export default throttle;