30秒学会 CSS 片段 – Scroll progress bar

Creates a progress bar indicating the scroll percentage of the page.

• Use position: fixed and a large z-index value to place the element at the top of the page and above any content.
• Use EventTarget.addEventListener() and Element.scrollTop to determine the scroll percentage of the document and apply it to the width of the element.

预览

HTML

<div id="scroll-progress"></div>

CSS

body {
  min-height: 200vh;
}

#scroll-progress {
  position: fixed;
  top: 0;
  width: 0%;
  height: 4px;
  background: #7983ff;
  z-index: 10000;
}

JavaScript

const scrollProgress = document.getElementById('scroll-progress');
const height =
  document.documentElement.scrollHeight - document.documentElement.clientHeight;

window.addEventListener('scroll', () => {
  const scrollTop =
    document.body.scrollTop || document.documentElement.scrollTop;
  scrollProgress.style.width = `${(scrollTop / height) * 100}%`;
});

翻译自：https://www.30secondsofcode.org/css/s/scroll-progress-bar