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React animation done right

Russian version

TL;DR use Web Animation API. Works only in Chrome, FF

There are some ways to animate DOM elements. The most old is the jQuery .animate(). Back in time it gave web-developers the holy grail: nice API and perfect browser support.

$("#book").animate({
  opacity: 0.25,
  left: "+=50",
  height: "toggle"
}, 5000, function() {
  // Animation completed
});

The animation is calculated in JS, which is both a plus (cross-browser) and a significant disadvantage regarding performance. Any complex animation started to slow down on a weak processor.

There are other libraries that use JS for DOM elements animations. Pros and cons are the same.

CSS to the rescue

It was obvious that a way was needed to enable the creation of performant animation, which could be accelerated by hardware. That’s why specification css3-animations was created.

The main difference was the declarative syntax based on CSS, which could describe the behavior of the elements. There are many advantages to this method. The main one is the support for hardware acceleration for obtaining 60 fps for animations. The downside is that it’s extremely inconvenient to use such animations from JS.

For example, to do something after the end of the animation, you have to listen the animationend and webkitAnimationEnd events on the element.

React way

From the very beginning, the developers of React suggested the way to animate components by setting the CSS classes to elements. And to handle addition and removal of elements they event created addon, which looks totally weird.

Here is an example from the official documentation:

<ReactCSSTransitionGroup
    transitionName="example"
    transitionEnterTimeout={500}
    transitionLeaveTimeout={300}>
    {items}
</ReactCSSTransitionGroup>

In addition to the component, you need to describe CSS:

.example-enter {
  opacity: 0.01;
}

.example-enter.example-enter-active {
  opacity: 1;
  transition: opacity 500ms ease-in;
}

.example-leave {
  opacity: 1;
}

.example-leave.example-leave-active {
  opacity: 0.01;
  transition: opacity 300ms ease-in;
}

There are different kinds of libraries that work similarly.

Web Animations API

Blink based browsers and Firefox already have the support for a new way to animate In Blink based browsers (Chrome, Opera, etc.) and in Firefox there is already elements — Web Animations API.

The component code can be:

const style = {
  background: '#f49',
  width: '100px',
  height: '100px',
  margin: '50px auto',
  color: 'white'
}

class Animated extends React.Component {
  run() {
    this.el.animate([
      { transform: 'scale(1)' },
      { transform: 'scale(1.3)' },
      { transform: 'scale(1)' }
    ], {
        duration: 400,
        iterations: 3
      })
  }

  render() {
    return <div onClick={this.run.bind(this)} ref={e => this.el = e} style={style}>
      Click me!
    </div>
  }
}

Live example.

In addition, to the declarative description of the animation, the execution time and the number of repetitions, you can specify the start delay, the type of animation, and other properties, which can be specified in CSS.

Element.animate returns an object of the type Animation. Which can be used to:

  • Subscribe to animation finish (with Promise)

    const animation = element.animate(keyframes, options)
    animation.finished.then(() => {
      console.log('Done!')
    })
    
  • Cancel animation
    animation.cancel()
    
  • Or event play it reversed
    animation.reverse()
    
  • Other cool stuff

Conclusion

Web animations API are a powerful animation management tool for JavaScript. It is extremely useful in the React components.

Unfortunately, given the support of browsers, it is impossible to use this method in production in most cases. However, if you are lucky and need to support only Chrome and FF, then Element.animate can be a good helper.

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