jaredkwright jaredkwright - 3 months ago 54
Javascript Question

How should I handle a leave animation in componentWillUnmount in React?

I was wondering if anyone could provide some insight about how they handle leave animations in React.js. I have been using Greensock TweenMax and the enter animations work fine on

componentDidMount
, but I haven't found a reliable way to animate a component out.

My feeling is that it should go in
componentWillUnmount
, but React provides no callback mechanism for you to indicate when you are ready to let go of a component. Therefore the transition animation never completes since the animations are asynchronous to React. Instead, you see a tiny fraction of a second of animation, the component disappears, and is replaced by the next component animating in.

This is a problem I have struggled with since I started using React 9 months ago. I can't help but think there has to be a solution out there other than
ReactCSSTransitionGroup
which I find to be cumbersome and finicky, especially with react-router.

Answer

ReactTransitionGroup (upon which ReactCSSTransitionGroup is built) is the base component that allows asynchronous entering and leaving. It provides lifecycle hooks that you can use to hook into JS-based animations. The docs list the allowed hooks:

ReactTransitionGroup is the basis for animations. It is accessible as React.addons.TransitionGroup. When children are declaratively added or removed from it (as in the example above) special lifecycle hooks are called on them.

componentWillAppear(callback)

This is called at the same time as componentDidMount() for components that are initially mounted in a TransitionGroup. It will block other animations from occurring until callback is called. It is only called on the initial render of a TransitionGroup.

componentDidAppear()

This is called after the callback function that was passed to componentWillAppear is called.

componentWillEnter(callback)

This is called at the same time as componentDidMount() for components added to an existing TransitionGroup. It will block other animations from occurring until callback is called. It will not be called on the initial render of a TransitionGroup.

componentDidEnter()

This is called after the callback function that was passed to componentWillEnter is called.

componentWillLeave(callback)

This is called when the child has been removed from the ReactTransitionGroup. Though the child has been removed, ReactTransitionGroup will keep it in the DOM until callback is called.

componentDidLeave()

This is called when the willLeave callback is called (at the same time as componentWillUnmount).

Animation - Low-level API

In order to animate a child out, you'd need to start your animation in componentWillLeave and call the provided callback when the animation is complete. As an example, here's a JSFiddle showing a component that stagger-animates its children in and out: http://jsfiddle.net/BinaryMuse/f51jbw2k/

The relevant code for animating out is:

componentWillLeave: function(callback) {
  this._animateOut(callback);
},

_animateOut(callback) {
  var el = React.findDOMNode(this);
  setTimeout(function() {
    TweenLite.to(el, 1, {opacity: 0}).play().eventCallback("onComplete", callback);
  }, this.props.animateOutDelay);
},
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