基本原理：
1、滚动到底部元素的滚动距离 + 元素的可视距离 == 元素的滚动条总距离2、滚动到顶部元素的滚动距离 == 0
监听页面滚动
<!DOCTYPE html><html lang="en"><head><meta charset="UTF-8" /><meta http-equiv="X-UA-Compatible" content="IE=edge" /><meta name="viewport" content="width=device-width, initial-scale=1.0" /><title>Scroll Demo</title></head><body><style>.box {height: 5000px;text-align: center;}</style><div class="box" id="box">打开控制台查看</div><!-- 引入节流方法 --><script src="/npm/throttle-debounce@5.0.0/umd/index.min.js"></script><script>// 滚动方向枚举值const DIRECTION_ENUM = {DOWN: "down",UP: "up",};// 距离顶部或底部的阈值const threshold = 20;// 记录前一个滚动位置let beforeScrollTop = 0;function handleScroll() {// 距顶部var scrollTop =document.documentElement.scrollTop || document.body.scrollTop;// 可视区高度var clientHeight =document.documentElement.clientHeight || document.body.clientHeight;// 滚动条总高度var scrollHeight =document.documentElement.scrollHeight || document.body.scrollHeight;// 打印数值console.table([{label: "距顶部",value: scrollTop,},{label: "可视区高度",value: clientHeight,},{label: "滚动条总高度",value: scrollHeight,},{label: "距顶部 + 可视区高度",value: scrollTop + clientHeight,},]);// 确定滚动方向let direction = DIRECTION_ENUM.DOWN;if (beforeScrollTop > scrollTop) {direction = DIRECTION_ENUM.UP;}// 通过滚动方向判断是触底还是触顶if (direction == DIRECTION_ENUM.DOWN) {// 滚动触底if (scrollTop + clientHeight + threshold >= scrollHeight) {console.log("滚动触底");}} else {// 滚动到顶部if (scrollTop <= threshold) {console.log("滚动到顶部");}}beforeScrollTop = scrollTop;}// 滚动节流const throttleHandleScroll = throttleDebounce.throttle(1000,handleScroll);// 监听滚动window.addEventListener('scroll', throttleHandleScroll);</script></body></html>
同理，也可以监听元素的滚动
<style>.box-wrap {height: 500px;overflow-y: auto;}.box {height: 5000px;text-align: center;}</style><div class="box-wrap" id="box"><div class="box">打开控制台查看</div></div><script>// 监听滚动let box = document.querySelector("#box");box.addEventListener("scroll", function (e) {let scrollTop = e.target.scrollTop;let clientHeight = e.target.clientHeight;let scrollHeight = e.target.scrollHeight;// 打印数值console.table([{label: "距顶部",value: scrollTop,},{label: "可视区高度",value: clientHeight,},{label: "滚动条总高度",value: scrollHeight,},{label: "距顶部 + 可视区高度",value: scrollTop + clientHeight,},]);});</script>
判断触底需要注意的点：
滚动时需要区分向上滚动还是向下滚动滚动时可以设置一个阈值，并非完全触底或触顶才触发滚动事件需要做节流操作，以免短时间内被多次触发
在线Demo
16.1、监听浏览器scroll滚动事件,触顶和触底16.2、监听元素scroll滚动事件,触顶和触底
参考
js 监听页面滚动到底部，监听可视区域滚动到底部
