手写防抖和节流函数

防抖

function debound(fn, delay) {
      let timer = null
      return function () {
        clearTimeout(timer)
        
        timer = setTimeout(() => {
          fn.apply(this, arguments)
        }, delay)
      }
    }

节流（三种）

 function throttle(fn, delay) {
      let cd = 0
      return function () {
        let now = Date.now()
        if (now - cd > delay) {
          fn.apply(this, arguments)
          cd = now
        }
      }
    }

 function throttle1(fn, delay) {
      let cd = true
      return function () {
        if (cd) {
          fn.apply(this, arguments)
          cd = false
          setTimeout(() => (cd = true), delay)
        }
      }
    }

 function throttle2(fn, delay) {
      let timer = null
      return function () {
        if (timer) return
        timer = setTimeout(() => {
          fn.apply(this, arguments)
          timer = null
        }, delay)
      }
    }