1. 防抖节流

防抖

• 事件被执行n秒后，再执行回调，如果n秒内又触发了，则重新计时

  function debounce(fn, delay) {
    let timer = null;
    return function(){
        cleatTimeout(timer);
        const self = this;
        const args = arguments;
        timer = setTimeout(() => {
            fn.apply(self, args);
        }, delay)
    }
  }

节流

• 每隔一段时间，执行一次

  function throttled(fn, delay) {
    const startTime = Date.now();
    let timer = null;
    return function(){
        const self = this;
        const args = arguments;
        clearTimeout(timer);
        let currentTime = Date.now();
        const remaining = delay - (currentTime - startTime);
        if(remaining < 0) {
            fn.apply(self, args);
            currentTime = Date.now();
        }else {
            timer = setTimeout(fn, delay)
        }
    }
  }