滚动条距离顶部的距离
let ele=document.getElementById("demo")
console.log(ele.scrollTop)
滚动条距离底部的距离
let ele=document.getElementById("demo")
console.log(ele.scrollHeight-ele.scrollTop-ele.clientHeight)
let ele=document.getElementById("demo")
console.log(ele.scrollTop)
let ele=document.getElementById("demo")
console.log(ele.scrollHeight-ele.scrollTop-ele.clientHeight)