The scroll-behavior property in CSS allows us to define whether the scroll location of the browser jumps to a new location or animates the transition when a user clicks a link that targets an anchored position within a scrolling box.
Smooth scrolling (the animated change of position within the viewport from the originating link to the destination anchor) can be a nice interaction detail added to a site, giving a polished feel to the experience. If you don't believe me, look at how many people have responded to the Smooth Scrolling snippet here on CSS-Tricks.
Native browser smooth scrolling is like this:
// Scroll to specific values
// scrollTo is the same
window.scroll({
top: 2500,
left: 0,
behavior: 'smooth'
});
// Scroll certain amounts from current position
window.scrollBy({
top: 100, // could be negative value
left: 0,
behavior: 'smooth'
});
// Scroll to a certain element
document.querySelector('.hello').scrollIntoView({
behavior: 'smooth'
});Dustan Kasten has a polyfill for this.
Whatever technology you use for smooth scrolling, accessibility is a concern. For example, if you click a #hash link, the native behavior is for the browser to change focus to the element matching that ID. The page may scroll, but the scrolling is a side effect of the focus changing.
If you override the default focus-changing behavior (which you have to, to prevent instant scrolling and enable smooth scrolling), you need to handle the focus-changing yourself.
Heather Migliorisi wrote about this, with code solutions, in Smooth Scrolling and Accessibility.
jQuery can also do this. Here's the code to perform a smooth page scroll to an anchor on the same page. It has some logic built in to identify those jump links, and not target other links.
// Select all links with hashes
$('a[href*="#"]')
// Remove links that don't actually link to anything
.not('[href="#"]')
.not('[href="#0"]')
.click(function(event) {
// On-page links
if (
location.pathname.replace(/^\//, '') == this.pathname.replace(/^\//, '')
&&
location.hostname == this.hostname
) {
// Figure out element to scroll to
var target = $(this.hash);
target = target.length ? target : $('[name=' + this.hash.slice(1) + ']');
// Does a scroll target exist?
if (target.length) {
// Only prevent default if animation is actually gonna happen
event.preventDefault();
$('html, body').animate({
scrollTop: target.offset().top
}, 1000, function() {
// Callback after animation
// Must change focus!
var $target = $(target);
$target.focus();
if ($target.is(":focus")) { // Checking if the target was focused
return false;
} else {
$target.attr('tabindex','-1'); // Adding tabindex for elements not focusable
$target.focus(); // Set focus again
};
});
}
}
});See the Pen Smooth Page Scrolling in jQuery by Chris Coyier (@chriscoyier) on CodePen.