[debounce] debounce and throttle #utils

debounce.js

function debounce(fn, delay) {
  let timer = setTimeout(fn, delay);
  return function(){
    clearTimeout(timer);
    fn.apply(this, arguments);
  };
}

function throttle(fn, delay) {
  let timer = setTimeout(fn, delay);
  let startTime = new Date();
  return function() {
    clearTimeout(timer);
    let currentTime = new Date();
    if(currentTime - startTime > delay) {
      fn.apply(this, arguments);
      startTime = currentTime;
    } else {
      timer = = setTimeout(fn, delay);
    }
  }
}