0
点赞
收藏
分享

微信扫一扫

js监听页面或元素scroll事件,滚动到底部或顶部

js监听页面或元素scroll事件,滚动到底部或顶部_javascript

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​​


举报

相关推荐

0 条评论