手写防抖函数（debounce）和节流函数（throttle）

debounce函数

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

throttle函数

// 方法一：定时器实现
const throttle = function(fn,delay) {
  let timer = null
  return function() {
    const context = this
    let args = arguments
    if(!timer) {
      timer = setTimeout(() => {
        fn.apply(context,args) 
        clearTimeout(timer) 
        timer = null;
      },delay)
    }
  }
}

// 方法二：时间戳
const throttle2 = function(fn, delay) {
  let preTime = Date.now()

  return function() {
      const context = this
      let args = arguments
      let doTime = Date.now()
      if (doTime - preTime >= delay) {
          fn.apply(context, args)
          preTime = Date.now()
      }
  }
}