js---小火箭回到顶部
比较粗糙，能到到效果，点击小火箭回到顶部，期间有小火箭的特效，
用到了css3的动画，JS的滚动事件
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
<style>
#firetop {
width: 148px;
height: 250px;
background: url(https://images.cnblogs.com/cnblogs_com/muyun123/1532955/o_rocket_button_up.png);
cursor: pointer;
position: fixed;
bottom: 0;
right: 0;
transition: bottom 1s;
display: none;
}
#firetop:hover {
background-position: -148px 0;
}
body {
width: 100%;
height: 7000px;
}
@keyframes move {
0% {
background-position: -296px 0;
}
100% {
background-position: -892px 0;
}
}
</style>
</head>
<body>
<div id="firetop"></div>
</body>
<script>
(function () {
var firetop = document.getElementById('firetop');
//当有滚动时触发事件
window.onscroll = function () {
var num = window.scrollY;//获取滚动条的移动距离
var num1 = window.innerHeight;//屏幕可视区的高度
if (num > 200) {
firetop.style.display = 'block';//让回到顶部的小火箭出现
} else if (num <= 0) {
firetop.style.bottom = num1 + 'px';//改变定位的位置
}
}
//点击事件
firetop.onclick = function () {
var scrolltop = window.scrollY;
var timer = setInterval(function () {//定时器启动
scrolltop -= 50;
if (scrolltop <= -window.innerHeight) {
firetop.style.display = 'none'; //小火箭隐藏
firetop.style.animation = ''; //清除动画
firetop.style.bottom = 0 + 'px'; //还原小火箭位置
clearInterval(timer);
}
window.scrollTo(0, scrolltop);//设置滚动条距离顶部的距离
}, 30);
this.style = 'animation:move 2s steps(4, end) infinite;'//给动画
}
})();
</script>
</html>
