// Tutorial //

A Page Progress Bar with JavaScript and CSS Variables

Published on December 20, 2016 · Updated on April 16, 2020
Default avatar

By Alligator.io

A Page Progress Bar with JavaScript and CSS Variables

While we believe that this content benefits our community, we have not yet thoroughly reviewed it. If you have any suggestions for improvements, please let us know by clicking the “report an issue“ button at the bottom of the tutorial.

Here’s how to accomplish a scroll progress bar that advances as you scroll though pages of a site. It’s a nice way to convey a progress indicator for readers to know how far along they are in a post.

It uses the power of CSS Variables, and the solution is adapted from part of this excellent talk by Lea Verou.

First, add the following markup right after the opening body tag:

<div class="progress"></div>

Then style this .progress element with something like this:

.progress {
  background: linear-gradient(to right, #F9EC31 var(--scroll), transparent 0);
  background-repeat: no-repeat;
  position: fixed;
  width: 100%;
  height: 4px;
  z-index: 1;
}

Notice how in the linear gradient we’re referring to a CSS variable named --scroll, which will be given a value on scroll.

That means that all that’s left to do is listen for the document’s scroll event and set the value of the --scroll custom property with the scroll percentage. We use element.style.setProperty for that. The .progress element will get an inline value for --scroll once it gets set.

Thanks to Phil Ricketts and his solution to this StackOverflow question for an accurate way to calculate the document scroll percentage:

var h = document.documentElement,
  b = document.body,
  st = 'scrollTop',
  sh = 'scrollHeight',
  progress = document.querySelector('.progress'),
  scroll;

document.addEventListener('scroll', function() {
  scroll = (h[st]||b[st]) / ((h[sh]||b[sh]) - h.clientHeight) * 100;
  progress.style.setProperty('--scroll', scroll + '%');
});

👉 Note that IE or Edge don’t support CSS custom properties at the moment. Support is coming however, and it the mean time the feature gracefully degrades.

Thanks for learning with the DigitalOcean Community. Check out our offerings for compute, storage, networking, and managed databases.

Learn more about us


About the authors
Default avatar
Alligator.io

author

Still looking for an answer?

Ask a questionSearch for more help

Was this helpful?
 
Leave a comment


This textbox defaults to using Markdown to format your answer.

You can type !ref in this text area to quickly search our full set of tutorials, documentation & marketplace offerings and insert the link!

Try DigitalOcean for free

Click below to sign up and get $200 of credit to try our products over 60 days!

Sign up

card icon
Get our biweekly newsletter

Sign up for Infrastructure as a Newsletter.

Sign up
card icon
Hollie's Hub for Good

Working on improving health and education, reducing inequality, and spurring economic growth? We’d like to help.

Learn more
card icon
Become a contributor

You get paid; we donate to tech nonprofits.

Learn more
Welcome to the developer cloud

DigitalOcean makes it simple to launch in the cloud and scale up as you grow – whether you’re running one virtual machine or ten thousand.

Learn more ->
DigitalOcean Cloud Control Panel
Get started for free

Sign up and get $200 in credit for your first 60 days with DigitalOcean.

This promotional offer applies to new account only.

© 2023 DigitalOcean, LLC.