Animation provides the illusion of motion: HTML elements change styling over time. Well-designed animations can make your application more fun and easier to use, but they aren't just cosmetic. Animations can improve your app and user experience in a number of ways:
Typically, animations involve multiple style *transformations* over time. An HTML element can move, change color, grow or shrink, fade, or slide off the page. These changes can occur simultaneously or sequentially. You can control the timing of each transformation.
Angular's animation system is built on CSS functionality, which means you can animate any property that the browser considers animatable. This includes positions, sizes, transforms, colors, borders, and more. The W3C maintains a list of animatable properties on its [CSS Transitions](https://www.w3.org/TR/css-transitions-1/) page.
The features described in this guide — and the more advanced features described in the related Angular animations guides — are demonstrated in an example app available as a <live-example></live-example>.
The main Angular modules for animations are `@angular/animations` and `@angular/platform-browser`. When you create a new project using the CLI, these dependencies are automatically added to your project.
In the component file, add a metadata property called `animations:` within the `@Component()` decorator. You put the trigger that defines an animation within the `animations` metadata property.
Let's animate a simple transition that changes a single HTML element from one state to another. For example, you can specify that a button displays either **Open** or **Closed** based on the user's last action. When the button is in the `open` state, it's visible and yellow. When it's in the `closed` state, it's transparent and green.
In HTML, these attributes are set using ordinary CSS styles such as color and opacity. In Angular, use the `style()` function to specify a set of CSS styles for use with animations. You can collect a set of styles in an animation state, and give the state a name, such as `open` or `closed`.
Use Angular's `state()` function to define different states to call at the end of each transition. This function takes two arguments: a unique name like `open` or `closed` and a `style()` function.
Use the `style()` function to define a set of styles to associate with a given state name. Note that the style attributes must be in [*camelCase*](guide/glossary#case-conventions).
Let's see how Angular's `state()` function works with the `style()` function to set CSS style attributes. In this code snippet, multiple style attributes are set at the same time for the state. In the `open` state, the button has a height of 200 pixels, an opacity of 1, and a background color of yellow.
In Angular, you can set multiple styles without any animation. However, without further refinement, the button instantly transforms with no fade, no shrinkage, or other visible indicator that a change is occurring.
To make the change less abrupt, we need to define an animation *transition* to specify the changes that occur between one state and another over a period of time. The `transition()` function accepts two arguments: the first argument accepts an expression that defines the direction between two transition states, and the second argument accepts one or a series of `animate()` steps.
Use the `animate()` function to define the length, delay, and easing of a transition, and to designate the style function for defining styles while transitions are taking place. You can also use the `animate()` function to define the `keyframes()` function for multi-step animations. These definitions are placed in the second argument of the `animate()` function.
The first part, `duration`, is required. The duration can be expressed in milliseconds as a simple number without quotes, or in seconds with quotes and a time specifier. For example, a duration of a tenth of a second can be expressed as follows:
The third argument, `easing`, controls how the animation [accelerates and decelerates](https://easings.net/) during its runtime. For example, `ease-in` causes the animation to begin slowly, and to pick up speed as it progresses.
* Run for 200ms, with no delay. Use a standard curve to start slow, accelerate in the middle, and then decelerate slowly at the end: `'0.2s ease-in-out'`
**Note:** See the Material Design website's topic on [Natural easing curves](https://material.io/design/motion/speed.html#easing) for general information on easing curves.
In the code snippet above, the `=>` operator indicates unidirectional transitions, and `<=>` is bidirectional. Within the transition, `animate()` specifies how long the transition takes. In this case, the state change from `open` to `closed` takes one second, expressed here as `1s`.
* You can include multiple state pairs within the same `transition()` argument:<br/>`transition( 'on => off, off => void' )`.
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### Triggering the animation
An animation requires a *trigger*, so that it knows when to start. The `trigger()` function collects the states and transitions, and gives the animation a name, so that you can attach it to the triggering element in the HTML template.
The `trigger()` function describes the property name to watch for changes. When a change occurs, the trigger initiates the actions included in its definition. These actions can be transitions or other functions, as we'll see later on.
In this example, we'll name the trigger `openClose`, and attach it to the `button` element. The trigger describes the open and closed states, and the timings for the two transitions.
**Note:** Within each `trigger()` function call, an element can only be in one state at any given time. However, it's possible for multiple triggers to be active at once.
Animations are defined in the metadata of the component that controls the HTML element to be animated. Put the code that defines your animations under the `animations:` property within the `@Component()` decorator.
When you've defined an animation trigger for a component, you can attach it to an element in that component's template by wrapping the trigger name in brackets and preceding it with an `@` symbol. Then, you can bind the trigger to a template expression using standard Angular property binding syntax as shown below, where `triggerName` is the name of the trigger, and `expression` evaluates to a defined animation state.
In this example, when the `isOpen` expression evaluates to a defined state of `open` or `closed`, it notifies the trigger `openClose` of a state change. Then it's up to the `openClose` code to handle the state change and kick off a state change animation.
For elements entering or leaving a page (inserted or removed from the DOM), you can make the animations conditional. For example, use `*ngIf` with the animation trigger in the HTML template.
**Note:** In the component file, set the trigger that defines the animations as the value of the `animations:` property in the `@Component()` decorator.
You can learn about more advanced features in Angular animations under the Animation section, beginning with advanced techniques in [transition and triggers](guide/transition-and-triggers).
The functional API provided by the `@angular/animations` module provides a domain-specific language (DSL) for creating and controlling animations in Angular applications. See the [API reference](api/animations) for a complete listing and syntax details of the core functions and related data structures.
<td>Kicks off the animation and serves as a container for all other animation function calls. HTML template binds to <code>triggerName</code>. Use the first argument to declare a unique trigger name. Uses array syntax.</td>
<td>Creates a named set of CSS styles that should be applied on successful transition to a given state. The state can then be referenced by name within other animation functions.</td>
<td>Specifies the timing information for a transition. Optional values for <code>delay</code> and <code>easing</code>. Can contain <code>style()</code> calls within.</td>
<td>Allows a sequential change between styles within a specified time interval. Use within <code>animate()</code>. Can include multiple <code>style()</code> calls within each <code>keyframe()</code>. Uses array syntax.</td>
<td>Specifies a group of animation steps (<em>inner animations</em>) to be run in parallel. Animation continues only after all inner animation steps have completed. Used within <code>sequence()</code> or <code>transition().</code></td>
Check out this [presentation](https://www.youtube.com/watch?v=rnTK9meY5us), shown at the AngularConnect conference in November 2017, and the accompanying [source code](https://github.com/matsko/animationsftw.in).
