JSFiddle - React, Tailwind, and code Playground

by 智翔

HTML

<div class="scrollbar">
	<div class="scrollbar-content">
		<ul class="box">
			<li>11111</li>
      <li>11111</li>
      <li>11111</li>
      <li>11111</li>
			<li>11111</li>
      <li>11111</li>
      <li>11111</li>
      <li>11111</li>
			<li>11111</li>
      <li>11111</li>
      <li>11111</li>
      <li>11111</li>
			<li>11111</li>
      <li>11111</li>
      <li>11111</li>
      <li>11111</li>
		</ul>
	</div>
	<div class='scrollbar-bar'>
		<div ref="thumb" class="scrollbar-thumb"></div>
	</div>
</div>
<button id="add">增加li</button>
<button id="del">删除li</button>

CSS

*{margin:0;padding:0;list-style: none;}
.scrollbar{
  position: relative;
}
.scrollbar-bar{
  position: absolute;
  right: 2px;
  bottom: 2px;
  z-index: 1;
  width: 6px;
  height: 100%;
  border-radius: 4px;
  opacity: 0;
  transition: opacity 120ms ease-out;
}
.scrollbar-thumb {
  position: relative;
  display: block;
  width: 100%;
  height: 0;
  border-radius: inherit;
  background-color: rgba(135,141,153,.3);
  transition: .3s background-color;
  cursor: pointer;
}
.scrollbar:hover .scrollbar-bar{
  opacity: 1;
  transition: opacity 340ms ease-out;
}
.box{ height: 400px;  overflow: auto; }
li{ line-height: 46px;  height: 46px; }

JavaScript

let wrap = document.getElementsByClassName("box")[0];
let bar = document.getElementsByClassName("scrollbar-bar")[0];
let thumb = document.getElementsByClassName("scrollbar-thumb")[0];

let gutter = getScrollWidth();{}
if(gutter){wrap.style.marginRight = `-${gutter}px`};
updateThumb()

function getScrollWidth(){
    const outer = document.createElement("div");
    outer.style.width = '100px';
    outer.style.visibility = "hidden";
    outer.style.position = "absolute";
    outer.style.top = "-9999px";
    document.body.appendChild(outer);

    const widthNoScroll = outer.offsetWidth;
    outer.style.overflow = "scroll";

    const inner = document.createElement("div");
    inner.style.width = "100%";
    outer.appendChild(inner);

    const widthWithScroll = inner.offsetWidth;
    outer.parentNode.removeChild(outer);
    scrollBarWidth = widthNoScroll - widthWithScroll;

    return scrollBarWidth;
}

function updateThumb(){
    let heightPercentage = (wrap.clientHeight * 100 / wrap.scrollHeight);
    thumb.style.height = heightPercentage + "%";   
}