@ngdoc tutorial
@name 14 - Animations
@step 14
@description

<ul doc-tutorial-nav="14"></ul>


In this step, we will enhance our web application by adding CSS and JavaScript animations on top of
the template code we created earlier.

* We now use the {@link ngAnimate ngAnimate} module to enable animations throughout the application.
* We also rely on built-in directives to automatically trigger hooks for animations to tap into.
* When an animation is found, it will run along with the actual DOM operation that is being issued
  on the element at the given time (e.g. inserting/removing nodes on {@link ngRepeat ngRepeat} or
  adding/removing classes on {@link ngClass ngClass}).


<div doc-tutorial-reset="14"></div>


## Dependencies

The animation functionality is provided by AngularJS in the `ngAnimate` module, which is distributed
separately from the core AngularJS framework. In addition we will use [jQuery][jquery] in this
project to do extra JavaScript animations.

Since we are using [npm][npm] to install client-side dependencies, this step updates the
`package.json` configuration file to include the new dependencies:

<br />
**`package.json`:**

```json
{
  "name": "angular-phonecat",
  ...
  "dependencies": {
    "angular": "1.8.x",
    "angular-animate": "1.8.x",
    "angular-resource": "1.8.x",
    "angular-route": "1.8.x",
    "bootstrap": "3.3.x",
    "jquery": "^3.5.1"
  },
  ...
}
```

* `"angular-animate": "1.8.x"` tells npm to install a version of the angular-animate module that
  is compatible with version 1.8.x of AngularJS.
* `"jquery": "^3.5.1"` tells npm to install a version of jQuery that is compatible with 3.5.x and at least 3.5.1.
  Note that this is not an AngularJS library; it is the standard jQuery library. We can use npm to
  install a wide range of 3rd party libraries.

Now, we must tell npm to download and install these dependencies.

```
npm install
```


## How Animations work with `ngAnimate`

To get an idea of how animations work with AngularJS, you might want to read the
[Animations](guide/animations) section of the Developer Guide first.


## Template

In order to enable animations, we need to update `index.html`, loading the necessary dependencies
(**angular-animate.js** and **jquery.js**) and the files that contain the CSS and JavaScript code
used in CSS/JavaScript animations. The animation module, {@link ngAnimate ngAnimate}, contains the
code necessary to make your application "animation aware".

<br />
**`app/index.html`:**

```html
  ...

  <!-- Defines CSS necessary for animations -->
  <link rel="stylesheet" href="app.animations.css" />

  ...

  <!-- Used for JavaScript animations (include this before angular.js) -->
  <script src="lib/jquery/dist/jquery.js"></script>

  ...

  <!-- Adds animation support in AngularJS -->
  <script src="lib/angular-animate/angular-animate.js"></script>

  <!-- Defines JavaScript animations -->
  <script src="app.animations.js"></script>

  ...
```

<div class="alert alert-error">
  **Important:** Be sure to use jQuery version 2.1 or newer, when using AngularJS 1.5 or newer;
  jQuery 1.x is not officially supported.
  In order for AngularJS to detect jQuery and take advantage of it, make sure to include `jquery.js`
  before `angular.js`.
</div>

Animations can now be created within the CSS code (`app.animations.css`) as well as the JavaScript
code (`app.animations.js`).


## Dependencies

We need to add a dependency on `ngAnimate` to our main module first:

<br />
**`app/app.module.js`:**

```js
  angular.
    module('phonecatApp', [
      'ngAnimate',
      ...
    ]);
```

Now that our application is "animation aware", let's create some fancy animations!


## CSS Transition Animations: Animating `ngRepeat`

We will start off by adding CSS transition animations to our `ngRepeat` directive present on the
`phoneList` component's template. We need to add an extra CSS class to our repeated element, in
order to be able to hook into it with our CSS animation code.

<br />
**`app/phone-list/phone-list.template.html`:**

```html
...
<ul class="phones">
  <li ng-repeat="phone in $ctrl.phones | filter:$ctrl.query | orderBy:$ctrl.orderProp"
      class="thumbnail phone-list-item">
    <a href="#!/phones/{{phone.id}}" class="thumb">
      <img ng-src="{{phone.imageUrl}}" alt="{{phone.name}}" />
    </a>
    <a href="#!/phones/{{phone.id}}">{{phone.name}}</a>
    <p>{{phone.snippet}}</p>
  </li>
</ul>
...
```

Did you notice the added `phone-list-item` CSS class? This is all we need in our HTML code to get
animations working.

Now for the actual CSS transition animation code:

<br />
**`app/app.animations.css`:**

```css
.phone-list-item.ng-enter,
.phone-list-item.ng-leave,
.phone-list-item.ng-move {
  transition: 0.5s linear all;
}

.phone-list-item.ng-enter,
.phone-list-item.ng-move {
  height: 0;
  opacity: 0;
  overflow: hidden;
}

.phone-list-item.ng-enter.ng-enter-active,
.phone-list-item.ng-move.ng-move-active {
  height: 120px;
  opacity: 1;
}

.phone-list-item.ng-leave {
  opacity: 1;
  overflow: hidden;
}

.phone-list-item.ng-leave.ng-leave-active {
  height: 0;
  opacity: 0;
  padding-bottom: 0;
  padding-top: 0;
}
```

As you can see, our `phone-list-item` CSS class is combined together with the animation hooks that
occur when items are inserted into and removed from the list:

* The `ng-enter` class is applied to the element when a new phone is added to the list and rendered
  on the page.
* The `ng-move` class is applied to the element when a phone's relative position in the list
  changes.
* The `ng-leave` class is applied to the element when a phone is removed from the list.

The phone list items are added and removed based on the data passed to the `ngRepeat` directive.
For example, if the filter data changes, the items will be animated in and out of the repeat list.

Something important to note is that, when an animation occurs, two sets of CSS classes are added to
the element:

1. A "starting" class that represents the style at the beginning of the animation.
2. An "active" class that represents the style at the end of the animation.

The name of the starting class is the name of the event that is fired (like `enter`, `move` or
`leave`) prefixed with `ng-`. So an `enter` event will result in adding the `ng-enter` class.

The active class name is derived from the starting class by appending an `-active` suffix.
This two-class CSS naming convention allows the developer to craft an animation, beginning to end.

In the example above, animated elements are expanded from a height of **0px** to **120px** when they
are added to the list and are collapsed back down to **0px** before being removed from the list.
There is also a catchy fade-in/fade-out effect that occurs at the same time. All this is handled by
the CSS transition declaration at the top of the CSS file.

<div class="alert alert-warning">
  Although all modern browsers have good support for [CSS transitions][caniuse-css-transitions] and
  [CSS animations][caniuse-css-animation], IE9 and earlier IE versions do not.
  If you want animations that are backwards-compatible with older browsers, consider using
  JavaScript-based animations, which are demonstrated below.
</div>


## CSS Keyframe Animations: Animating `ngView`

Next, let's add an animation for transitions between route changes in
{@link ngRoute.directive:ngView ngView}.

Again, we need to prepare our HTML template by adding a new CSS class, this time to the `ng-view`
element. In order to gain more "expressive power" for our animations, we will also wrap the
`[ng-view]` element in a container element.

<br />
**`app/index.html`:**

```html
<div class="view-container">
  <div ng-view class="view-frame"></div>
</div>
```

We have applied a `position: relative` CSS style to the `.view-container` wrapper, so that it is
easier for us to manage the `.view-frame` element's positioning during the animation.

With our preparation code in place, let's move on to the actual CSS styles for this transition
animation.

<br />
**`app/app.animations.css`:**

```css
...

.view-container {
  position: relative;
}

.view-frame.ng-enter,
.view-frame.ng-leave {
  background: white;
  left: 0;
  position: absolute;
  right: 0;
  top: 0;
}

.view-frame.ng-enter {
  animation: 1s fade-in;
  z-index: 100;
}

.view-frame.ng-leave {
  animation: 1s fade-out;
  z-index: 99;
}

@keyframes fade-in {
  from { opacity: 0; }
  to   { opacity: 1; }
}

@keyframes fade-out {
  from { opacity: 1; }
  to   { opacity: 0; }
}

/* Older browsers might need vendor-prefixes for keyframes and animation! */
```

Nothing fancy here! Just a simple fade-in/fade-out effect between pages. The only thing out of the
ordinary here is that we are using absolute positioning to position the entering page (identified
by the `ng-enter` class) on top of the leaving page (identified by the `ng-leave` class). At the
same time a cross-fade animation is performed. So, as the previous page is just about to be removed,
it fades out, while the new page fades in right on top of it.

Once the `leave` animation is over, the element is removed from the DOM. Likewise, once the `enter`
animation is complete, the `ng-enter` and `ng-enter-active` CSS classes are removed from the
element, causing it to rerender and reposition itself with its default CSS styles (so no more
absolute positioning once the animation is over). This works fluidly and the pages flow naturally
between route changes, without anything jumping around.

The applied CSS classes are much the same as with `ngRepeat`. Each time a new page is loaded the
`ngView` directive will create a copy of itself, download the template and append the contents. This
ensures that all views are contained within a single HTML element, which allows for easy animation
control.

For more on CSS animations, see the [MDN web docs][mdn-animations].


## Animating `ngClass` with JavaScript

Let's add another animation to our application. On our `phone-detail.template.html` view, we have a
nice thumbnail swapper. By clicking on the thumbnails listed on the page, the profile phone image
changes. But how can we incorporate animations?

Let's give it some thought first. Basically, when a user clicks on a thumbnail image, they are
changing the state of the profile image to reflect the newly selected thumbnail image. The best way
to specify state changes within HTML is to use classes. Much like before &mdash; when we used a CSS
class to drive the animation &mdash; this time the animation will occur when the CSS class itself
changes.

Every time a phone thumbnail is selected, the state changes and the `.selected` CSS class is added
to the matching profile image. This will trigger the animation.

We will start by tweaking our HTML code in `phone-detail.template.html`. Notice that we have changed
the way we display our large image:

<br />
**`app/phone-detail/phone-detail.template.html`:**

```html
<div class="phone-images">
  <img ng-src="{{img}}" class="phone"
      ng-class="{selected: img === $ctrl.mainImageUrl}"
      ng-repeat="img in $ctrl.phone.images" />
</div>

...
```

Just like with the thumbnails, we are using a repeater to display **all** the profile images as a
list, however we're not animating any repeat-related transitions. Instead, we will be keeping our
eye on each element's classes and especially the `selected` class, since its presence or absence
will determine if the element is visible or hidden. The addition/removal of the `selected` class is
managed by the {@link ngClass ngClass} directive, based on the specified condition
(`img === $ctrl.mainImageUrl`).
In our case, there is always exactly one element that has the `selected` class, and therefore there
will be exactly one phone profile image visible on the screen at all times.

When the `selected` class is added to an element, the `selected-add` and `selected-add-active`
classes are added just before to signal AngularJS to fire off an animation. When the `selected`
class is removed from an element, the `selected-remove` and `selected-remove-active` classes are
applied to the element, triggering another animation.

Finally, in order to ensure that the phone images are displayed correctly when the page is first
loaded, we also tweak the detail page CSS styles:

<br />
**`app/app.css`:**

```css
...

.phone {
  background-color: white;
  display: none;
  float: left;
  height: 400px;
  margin-bottom: 2em;
  margin-right: 3em;
  padding: 2em;
  width: 400px;
}

.phone:first-child {
  display: block;
}

.phone-images {
  background-color: white;
  float: left;
  height: 450px;
  overflow: hidden;
  position: relative;
  width: 450px;
}

...
```

You may be thinking that we are just going to create another CSS-based animation. Although we could
do that, let's take the opportunity to learn how to create JavaScript-based animations with the
{@link ng.angular.Module#animation .animation()} module method.

<br />
**`app/app.animations.js`:**

```js
  angular.
    module('phonecatApp').
    animation('.phone', function phoneAnimationFactory() {
      return {
        addClass: animateIn,
        removeClass: animateOut
      };

      function animateIn(element, className, done) {
        if (className !== 'selected') return;

        element.
          css({
            display: 'block',
            position: 'absolute',
            top: 500,
            left: 0
          }).
          animate({
            top: 0
          }, done);

        return function animateInEnd(wasCanceled) {
          if (wasCanceled) element.stop();
        };
      }

      function animateOut(element, className, done) {
        if (className !== 'selected') return;

        element.
          css({
            position: 'absolute',
            top: 0,
            left: 0
          }).
          animate({
            top: -500
          }, done);

        return function animateOutEnd(wasCanceled) {
          if (wasCanceled) element.stop();
        };
      }
    });
```

We are creating a custom animation by specifying the target elements via a CSS class selector (here
`.phone`) and an animation _factory_ function (here `phoneAnimationFactory()`). The factory function
returns an object associating specific _events_ (object keys) to animation _callbacks_ (object
values). The _events_ correspond to DOM actions that `ngAnimate` recognizes and can hook into, such
as `addClass`/`removeClass`/`setClass`, `enter`/`move`/`leave` and `animate`. The associated
callbacks are called by `ngAnimate` at appropriate times.

For more info on animation factories, check out the
{@link ng.$animateProvider#register API Reference}.

In this case, we are interested in a class getting added to/removed from a `.phone` element, thus we
specify callbacks for the `addClass` and `removeClass` events. When the `selected` class is added to
an element (via the `ngClass` directive), the `addClass` JavaScript callback will be executed with
`element` passed in as a parameter. The last parameter passed in is the `done` callback function. We
call `done()` to let AngularJS know that our custom JavaScript animation has ended. The `removeClass`
callback works the same way, but instead gets executed when a class is removed.

Note that we are using [jQuery][jquery]'s `animate()` helper to implement the animation. jQuery
isn't required to do JavaScript animations with AngularJS, but we use it here anyway in order to
keep the example simple. More info on `jQuery.animate()` can be found in the
[jQuery documentation][jquery-animate].

Within the event callbacks, we create the animation by manipulating the DOM. In the code above,
this is achieved using `element.css()` and `element.animate()`. As a result the new element is
positioned with an offset of **500px** and then both elements &mdash; the previous and the new
&mdash; are animated together by shifting each one up by **500px**. The outcome is a conveyor-belt
like animation. After the `animate()` function has completed the animation, it calls `done` to
notify AngularJS.

You may have noticed that each animation callback returns a function. This is an **optional**
function, which (if provided) will be called when the animation ends, either because it ran to
completion or because it was canceled (for example another animation took place on the same
element). A boolean parameter (`wasCanceled`) is passed to the function, letting the developer know
if the animation was canceled or not. Use this function to do any necessary clean-up.


## Experiments

<div></div>

* Reverse the animation, so that the elements animate downwards.

* Make the animation run faster or slower, by passing a `duration` argument to `.animate()`:

  ```js
  element.css({...}).animate({...}, 1000 /* 1 second */, done);
  ```

* Make the animations "asymmetrical". For example, have the previous element fade out, while the new
  element zooms in:

  ```js
  // animateIn()
  element.css({
    display: 'block',
    opacity: 1,
    position: 'absolute',
    width: 0,
    height: 0,
    top: 200,
    left: 200
  }).animate({
    width: 400,
    height: 400,
    top: 0,
    left: 0
  }, done);

  // animateOut()
  element.animate({
    opacity: 0
  }, done);
  ```

* Go crazy and come up with your own funky animations!


## Summary

Our application is now much more pleasant to use, thanks to the smooth transitions between pages
and UI states.

There you have it! We have created a web application in a relatively short amount of time. In the
{@link the_end closing notes} we will cover where to go from here.


<ul doc-tutorial-nav="14"></ul>


[caniuse-css-animation]: https://caniuse.com/#feat=css-animation
[caniuse-css-transitions]: https://caniuse.com/#feat=css-transitions
[jquery]: https://jquery.com/
[jquery-animate]: https://api.jquery.com/animate
[mdn-animations]: https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_Animations/Using_CSS_animations
[npm]: https://www.npmjs.com/
