<!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>
html, body {
height: 100%;
margin: 0;
}
#container {
position: absolute;
top: 50px;
left: 100px;
height: 400px;
width: 150px;
background-color: aliceblue;
padding: 2rem;
box-sizing: border-box;
/*必须属性，否则给scrollTop赋值无效*/
overflow-y: hidden;
position: relative;
padding-right: 30px;
}
.scrollbar {
height: 50px;
width: 10px;
border-radius: 20px;
background: #ccc;
position: absolute;
right: 0;
}
</style>
<script>
window.onload = function () {
var scrollbar = document.querySelector('.scrollbar');
var container = scrollbar.parentNode;
container.scrollbar = scrollbar;
container.ratio =
(container.scrollHeight - container.offsetHeight) / (container.offsetHeight - scrollbar.offsetHeight);
container.addEventListener('mousewheel', function(e) {
this.scrollTop += e.deltaY;
this.scrollbar.style.top = (this.scrollTop + this.scrollTop / this.ratio) + 'px';
});
container.addEventListener('mousedown', function (e) {
if (e.target === this.scrollbar) {
this.prevY = e.pageY;
}
});
container.addEventListener('mouseup', function (e) {
this.prevY = null;
});
container.addEventListener('mousemove', function (e) {
if (this.prevY) {
this.scrollTop += (e.pageY - this.prevY) * this.ratio;
this.scrollbar.style.top = (this.scrollTop + this.scrollTop / this.ratio) + 'px';
this.prevY = e.pageY;
}
e.preventDefault();
});
}
</script>
</head>
<body>
<div id="container">
<div class="scrollbar"></div>
<p>fefe</p>
<p>fefe</p>
<p>fefe</p>
<p>fefe</p>
<p>fefe</p>
<p>fefe</p>
<p>fefe</p>
<p>fefe</p>
<p>fefe</p>
<p>fefe</p>
<p>fefe</p>
<p>fefe</p>
<p>fefe</p>
<p>fefe</p>
<p>fefe</p>
<p>fefe</p>
<p>fefe</p>
<p>fefe</p>
<p>fefe</p>
<p>fefe</p>
<p>fefe</p>
</div>
</body>
</html>
