README

smoothscroll-anchor-polyfill

⚓ Apply smooth scroll to anchor links to polyfill the CSS property scroll-behavior

Features

✔ Smooth scroll to target when clicking an anchor
✔ Smooth scroll to target on hashchange (◀/▶ buttons)
✔ Updates URL with #fragment
✔ Handles focus for improved accessibility
✔ Doesn't break server-side rendering
✔ 1.3KB gzipped

⚠ Requires smooth scroll for window.scroll() and Element.scrollIntoView() (e.g. smoothscroll-polyfill) to work!

Browser support

IE / Edge	Firefox	Chrome	Safari	iOS Safari	Opera
IE9+, Edge	native	native*	last 2 versions	last 2 versions	native*

* hashchange navigation triggered by forwards/backwards buttons isn't smooth despite native support. Learn more

Usage

1. Set `scroll-behavior: smooth` in CSS

⚠ Has to be set global (on html), check the docs for limitations

Because CSS properties unknown to a browser can't efficiently be parsed from JavaScript, just specyfing the normal scroll-behavior property is not enough unfortunately.
You need to add an additional CSS variable so the polyfill can read it:

html {
  --scroll-behavior: smooth;
  scroll-behavior: smooth;
}

You can also use media queries, toggle classes etc. to control the smooth scroll. The following only enables smooth scroll on Desktop devices, for example:

html {
  --scroll-behavior: auto;
  scroll-behavior: auto;
}

@media screen and (min-width: 1150px) {
  html {
    --scroll-behavior: smooth;
    scroll-behavior: smooth;
  }
}

💡 This process can be automated using a PostCSS plugin, so you can write regular CSS and it'll be transformed to work with the polyfill automatically.
The plugin will also read your browserslist and choose the right transformation depending on if all your browsers support CSS variables or not. It just works™

Need to support Internet Explorer?

Legacy browsers like Internet Explorer do not support CSS variables, so you need another way to specify scroll-behavior. There are two options:

Using the inline `style` attribute

<html style="scroll-behavior: smooth;">
  ...
</html>

Using `font-family`

Alternatively, you can specify the property as the name of a custom font family. Your actual fonts will still work the way they should (plus, you can simply declare actual fonts on body). As with CSS variables (and unlike inline styles), this allows you to use normal CSS features like media queries.

<style>
  html {
    scroll-behavior: auto;
    font-family: 'scroll-behavior: auto;', 'Roboto', sans-serif;
  }
</style>

2. Install the polyfill

Because this polyfill only wires up anchor links to use the browser's native window.scroll() and element.scrollIntoView() methods, you'll need to load a polyfill providing smooth scroll to these methods in addition to the steps outlined below.

smoothscroll-polyfill works, but you can just as well use another one or write your own implementation. Learn More

2a. From a CDN

<script src="https://unpkg.com/smoothscroll-anchor-polyfill"></script>

2b. From npm

npm install smoothscroll-anchor-polyfill

then

import 'smoothscroll-anchor-polyfill'

Full Documentation & Demo

The full documentation with advanced installation instructions, limitations, features like enabling and disabling the smooth scrolling and more can be found at jonaskuske.github.io/smoothscroll-anchor-polyfill.
The documentation site itself is built as a smooth scrolling one-page design, utilizing this polyfill.

PRs welcome!

Usage no npm install needed!