JavaScript 返回顶部实例

2020-05-12 前端js 133

```css
<style>
#myBtn {
  display: none;
  position: fixed;
  bottom: 20px;
  right: 30px;
  z-index: 99;
  border: none;
  outline: none;
  background-color: red;
  color: white;
  cursor: pointer;
  padding: 15px;
  border-radius: 10px;
}
#myBtn:hover {
  background-color: #555;
}
</style>
<button onclick="topFunction()" id="myBtn" title="回顶部">返回顶部</button>
<div style="background-color:black;color:white;padding:30px">向下滑动</div>
<div style="background-color:lightgrey;padding:30px 30px 2500px">该实例演示了如何实现网页返回顶部效果。</div>
<script>
// 当网页向下滑动 20px 出现"返回顶部" 按钮
window.onscroll = function() {scrollFunction()};
function scrollFunction() {console.log(121);
    if (document.body.scrollTop > 20 || document.documentElement.scrollTop > 20) {
        document.getElementById("myBtn").style.display = "block";
    } else {
        document.getElementById("myBtn").style.display = "none";
    }
}
// 点击按钮，返回顶部
function topFunction() {
    document.body.scrollTop = 0;
    document.documentElement.scrollTop = 0;
}
</script>
```
还有一个简单的例子
```
#bb111 {
    position: fixed;
    bottom: 5px;
    right: 5px;
}
```
html
```
<div id="bb111">
<a href="javascript:;" id="dingbu" style="display: none;">▲</a>
</div>
```
```css
<script>
window.onscroll = function() {scrollFunction()};
function scrollFunction() {console.log(121);
    if (document.body.scrollTop > 100 || document.documentElement.scrollTop > 100) {
        document.getElementById("dingbu").style.display = "block";
    } else {
        document.getElementById("dingbu").style.display = "none";

}
}
	$("#dingbu").click(function(){
		//点击“回到顶部”，滚动到顶部，并带动画效果
			$("html,body").animate({scrollTop:0},500);
		});	  
</script>
```