节流与防抖

节流（一段时间执行一次之后，就不执行第二次）

 function throttle(fn, delay){
     let canUse = true
     return function(){
         if(canUse){
             fn.apply(this, arguments)
             canUse = false
             setTimeout(()=>canUse = true, delay)
         }
     }
 }
 const throttled = throttle(()=>console.log('hi'))
 throttled()
 throttled()

防抖（一段时间会等，然后带着一起做了）

 function debounce(fn, delay){
     let timerId = null
     return function(){
         const context = this
         if(timerId){window.clearTimeout(timerId)}
         timerId = setTimeout(()=>{
             fn.apply(context, arguments)
             timerId = null
         },delay)
     }
 }
 const debounced = debounce(()=>console.log('hi'))
 debounced()
 debounced()