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="https://cdn.jsdelivr.net/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