An Overview of Scroll Technologies

Choosing the Right Scroll Technology

Scroll-driven animations have become increasingly common on the web, aided by more capable devices. The available technologies fall into two rough categories: those that handle a single, well-defined scroll behavior, and those that let you build generic scroll-linked animations. Understanding which category your use case falls into is the first step in picking a tool.

Native CSS for Specific Behaviors

Modern browsers ship with a handful of native CSS features that cover simple scroll effects. For narrow use cases, they may be all you need.

Sticky Positioning and Parallax

When an element only needs to remain fixed during a portion of the page, position: sticky works well. It is built into modern browsers, though IE and some mobile browsers require a polyfill.

Pure CSS parallax is more of a technique than a technology. It is a handy approach when distinct page layers should move at different speeds, but getting the perspective and transform values right can be unintuitive. Numerous examples, such as the Firewatch-style header on CodePen, demonstrate the approach.

Scroll Snap and Smooth Scrolling

CSS scroll snap lets the browser settle on designated scroll positions once the user finishes scrolling, which keeps specific elements in view. The specification is still evolving, so check for the latest API details before relying on it in production.

Native smooth scrolling works when jumping between in-page anchors via window.scrollTo() or the scroll-behavior CSS property. Smoothing mouse-wheel input, however, is not natively supported across all browsers. JavaScript libraries that attempt this are often buggy and can conflict with other scroll tooling — and smooth scrolling is not always desirable in the first place.

Generic Scroll Animations

There is currently no CSS-only route to fire arbitrary animations based on scroll position or to scrub through an animation timeline (a specification proposal exists but is not imminent). Generic scroll effects therefore require JavaScript, which offers two broad strategies.

Intersection Observers

IntersectionObserver is well-suited for animations that depend on whether an element has entered the viewport and how much of it is visible. Reveal-on-scroll effects are a natural fit. However, it is awkward for triggering different animations based on scroll direction and of little use when an element needs to animate while it is fully in view between entry and exit points.

The Scroll Event

Listening to the scroll event gives the most control. An effect can be tied to any scroll position, with start and end points defined precisely for the project. The downsides are well known: unthrottled handlers hurt performance, and the event provides no convenient API for common behaviors. This is where scrolling libraries help — they handle throttling, resizing, and offer a friendlier interface.

Libraries for Full Control

Several libraries aim to deliver complete control over scroll-linked animations without requiring you to manually process scroll positions.

ScrollMagic and ScrollScene

ScrollMagic offers a relatively simple API for scroll effects and integrates with animation libraries such as GSAP and Velocity.js. Its maintenance slowed in recent years, prompting the creation of ScrollScene — a wrapper that improves ScrollMagic's usability and builds on a more actively maintained fork. ScrollScene adds video playback support along with scene init and duration breakpoints, and works with GSAP.

GSAP ScrollTrigger

ScrollTrigger is GreenSock's official plugin for GSAP. Its feature set is extensive, and its API is approachable: you define where animations begin and end, animate anything (DOM, SVG, canvas, WebGL), pin elements during the animation, and integrate smoothly with smooth-scrolling libraries. It also benefits from GreenSock's support and forums.

Locomotive Scroll

Locomotive Scroll is less comprehensive than the libraries above and focuses on custom smooth scrolling. It also allows animating specific DOM properties via data attributes or through its onscroll event for other object types.

Matching Tools to Effects

For specific effects such as sticky positioning and parallax, native CSS may be sufficient, ideally with polyfills where needed. For everything else, GSAP's ScrollTrigger is a strong default: it covers what CSS properties can do while handling browser compatibility and the underlying calculations.