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Bringing Pages to Life with the Web Animations API

This article is by guest author Dudley Storey. SitePoint guest posts aim to bring you engaging content from prominent writers and speakers of the JavaScript community.

One API to Rule Them All

Animation on the web has long been divided into four disparate camps:

  • CSS transitions and animations are very performant and provide keyframing, but are also time-consuming to build, and provide only basic start-and-end control in CSS and JavaScript. This has tended to relegate them to simple UI response animations, loops, and page load animations.
  • SMIL (Synchronized Multimedia Integration Language) is very powerful, but it’s also syntax-heavy and has incomplete browser support. It’s also limited to controlling elements solely inside the context of SVG.
  • JavaScript offers direct control of elements, but has no understanding of designer-friendly functions like keyframes or easing, and lacks the native optimization and performance of CSS. Canvas API animation is wonderful, but still lacks an understanding of animation fundamentals, and can’t animate arbitrary DOM elements.
  • JavaScript animation frameworks like Greensock attempt to pave over the traditional deficits of JavaScript when it comes to animation, but have all the associated drawbacks of frameworks: page load, performance, and learning a new syntax.

The Web Animations API seeks to integrate the best features of all of these into a single, unified specification, while eliminating the drawbacks, creating a native understanding of keyframes, easing, and element control in JavaScript, with the same on-screen performance as CSS. With core components of the specification now supported in Chrome and Firefox, and development either announced or underway in other browsers, including Safari and Edge, together with the availability of a robust polyfill, it’s time to give the Web Animations API serious consideration for bringing web pages to life.

Keyframes in JavaScript

Let’s take one of the simplest possible examples of a keyframe animation: moving a red ball element from one side of the page to the other. Regardless of which technique we use, the element will be the same:

<div id="redball"></div>

As will the initial CSS:

body {
  margin: 0;
  background: #000;
  overflow: hidden;
  min-height: 100vh;

#redball {
  background: red;
  width: 30vmin;
  height: 30vmin;
  border-radius: 50%;

I’ve used vmin units so that the element always remains symmetrical while responding to the size of the viewport.

In CSS, moving the ball from one side of the page to the other would require something like the following:

@keyframes moveBall {
  from {
    transform: translateX(-20vw);
  to {
    transform: translateX(100vw);

This animation would be called from the declaration for the red ball element:

#redball { 
  animation: moveBall 3s infinite;

The result, shown in Codepen:

See the Pen Basic CSS Red Ball Animation by SitePoint (@SitePoint) on CodePen.

There are a few things to note about the animation at this point, including the fact that easing (speeding up at the beginning and slowing down at the end) is automatically built in.

Enter the Web Animations API

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