---
id: animation
title: Animation
permalink: animation.html
prev: addons.html
next: two-way-binding-helpers.html
---

React provides a `ReactTransitionGroup` addon component as a low-level API for animation, and a `ReactCSSTransitionGroup` for easily implementing basic CSS animations and transitions.

## High-level API: `ReactCSSTransitionGroup`

`ReactCSSTransitionGroup` is based on `ReactTransitionGroup` and is an easy way to perform CSS transitions and animations when a React component enters or leaves the DOM. It's inspired by the excellent [ng-animate](http://www.nganimate.org/) library.

### Getting Started

`ReactCSSTransitionGroup` is the interface to `ReactTransitions`. This is a simple element that wraps all of the components you are interested in animating. Here's an example where we fade list items in and out.

```javascript{30-32}
/** @jsx React.DOM */

var ReactCSSTransitionGroup = React.addons.CSSTransitionGroup;

var TodoList = React.createClass({
  getInitialState: function() {
    return {items: ['hello', 'world', 'click', 'me']};
  },
  handleAdd: function() {
    var newItems =
      this.state.items.concat([prompt('Enter some text')]);
    this.setState({items: newItems});
  },
  handleRemove: function(i) {
    var newItems = this.state.items;
    newItems.splice(i, 1);
    this.setState({items: newItems});
  },
  render: function() {
    var items = this.state.items.map(function(item, i) {
      return (
        <div key={item} onClick={this.handleRemove.bind(this, i)}>
          {item}
        </div>
      );
    }.bind(this));
    return (
      <div>
        <button onClick={this.handleAdd}>Add Item</button>
        <ReactCSSTransitionGroup transitionName="example">
          {items}
        </ReactCSSTransitionGroup>
      </div>
    );
  }
});
```

In this component, when a new item is added to `ReactCSSTransitionGroup` it will get the `example-enter` CSS class and the `example-enter-active` CSS class added in the next tick. This is a convention based on the `transitionName` prop.

You can use these classes to trigger a CSS animation or transition. For example, try adding this CSS and adding a new list item:

```css
.example-enter {
  opacity: 0.01;
  transition: opacity .5s ease-in;
}

.example-enter.example-enter-active {
  opacity: 1;
}
```

You'll notice that when you try to remove an item `ReactCSSTransitionGroup` keeps it in the DOM. If you're using an unminified build of React with add-ons you'll see a warning that React was expecting an animation or transition to occur. That's because `ReactCSSTransitionGroup` keeps your DOM elements on the page until the animation completes. Try adding this CSS:

```css
.example-leave {
  opacity: 1;
  transition: opacity .5s ease-in;
}

.example-leave.example-leave-active {
  opacity: 0.01;
}
```

### Animation Group Must Be Mounted To Work

In order for it to apply transitions to its children, the `ReactCSSTransitionGroup` must already be mounted in the DOM. The example below would not work, because the `ReactCSSTransitionGroup` is being mounted along with the new item, instead of the new item being mounted within it. Compare this to the [Getting Started](#getting-started) section above to see the difference.

```javascript{12-14}
  render: function() {
    var items = this.state.items.map(function(item, i) {
      return (
        <div key={item} onClick={this.handleRemove.bind(this, i)}>
          <ReactCSSTransitionGroup transitionName="example">
            {item}
          </ReactCSSTransitionGroup>
        </div>
      );
    }, this);
    return (
      <div>
        <button onClick={this.handleAdd}>Add Item</button>
        {items}
      </div>
    );
  }
```

### Animating One or Zero Items

Although in the example above we rendered a list of items into `ReactCSSTransitionGroup`, the children of `ReactCSSTransitionGroup` can be one or zero items. This makes it possible to animate a single element entering or leaving. Similarly, you can animate a new element replacing the current element, with the new element animating in while the current animates out. For example, we can implement a simple image carousel like this:

```javascript{12-14}
/** @jsx React.DOM */

var ReactCSSTransitionGroup = React.addons.CSSTransitionGroup;

var ImageCarousel = React.createClass({
  propTypes: {
    imageSrc: React.PropTypes.string.isRequired
  },
  render: function() {
    return (
      <div>
        <ReactCSSTransitionGroup transitionName="carousel">
          <img src={this.props.imageSrc} key={this.props.imageSrc} />
        </ReactCSSTransitionGroup>
      </div>
    );
  }
});
```

> Note:
>
> You must provide [the `key` attribute](/react/docs/multiple-components.html#dynamic-children) for all children of `ReactCSSTransitionGroup`, even if rendering a single item. This is how React will determine which children have entered, left, or stayed.

### Disabling Animations

You can disable animating `enter` or `leave` animations if you want. For example, sometimes you may want an `enter` animation and no `leave` animation, but `ReactCSSTransitionGroup` waits for an animation to complete before removing your DOM node. You can add `transitionEnter={false}` or `transitionLeave={false}` props to `ReactCSSTransitionGroup` to disable these animations.

> Note:
>
> When using `ReactCSSTransitionGroup`, there's no way for your components to be notified when a transition has ended or to perform any more complex logic around animation. If you want more fine-grained control, you can use the lower-level `ReactTransitionGroup` API which provides the hooks you need to do custom transitions.

## Low-level API: `ReactTransitionGroup`

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

### `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`).

### Rendering a Different Component

By default `ReactTransitionGroup` renders as a `span`. You can change this behavior by providing a `component` prop. For example, here's how you would render a `<ul>`:

```javascript{1}
<ReactTransitionGroup component={React.DOM.ul}>
  ...
</ReactTransitionGroup>
```

Every DOM component is under `React.DOM`. However, `component` does not need to be a DOM component. It can be any React component you want; even ones you've written yourself!
