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# `ngAnimate`

The `ngAnimate` module provides support for CSS-based animations (keyframes and transitions) as well as JavaScript-based animations via callback hooks. Animations are not enabled by default, however, by including `ngAnimate` then the animation hooks are enabled for an Angular app.

# Usage

Simply put, there are two ways to make use of animations when ngAnimate is used: by using CSS and JavaScript. The former works purely based using CSS (by using matching CSS selectors/styles) and the latter triggers animations that are registered via `module.animation()`. For both CSS and JS animations the sole requirement is to have a matching `CSS class` that exists both in the registered animation and within the HTML element that the animation will be triggered on.

## Directive Support

The following directives are "animation aware":

Directive | Supported Animations
--- | ---
ngRepeat | enter, leave and move
ngView | enter and leave
ngInclude | enter and leave
ngSwitch | enter and leave
ngIf | enter and leave
ngClass | add and remove (the CSS class(es) present)
ngShow & ngHide | add and remove (the ng-hide class value)
form & ngModel | add and remove (dirty, pristine, valid, invalid & all other validations)
ngMessages | add and remove (ng-active & ng-inactive)
ngMessage | enter and leave

(More information can be found by visiting each the documentation associated with each directive.)

## CSS-based Animations

CSS-based animations with ngAnimate are unique since they require no JavaScript code at all. By using a CSS class that we reference between our HTML and CSS code we can create an animation that will be picked up by Angular when an the underlying directive performs an operation.

The example below shows how an `enter` animation can be made possible on a element using `ng-if`:

    <div ng-if="bool" class="fade">
       Fade me in out
    </div>
    <button ng-click="bool=true">Fade In!</button>
    <button ng-click="bool=false">Fade Out!</button>

Notice the CSS class fade? We can now create the CSS transition code that references this class:

    /* The starting CSS styles for the enter animation */
    .fade.ng-enter {
      transition:0.5s linear all;
      opacity:0;
    }

    /* The finishing CSS styles for the enter animation */
    .fade.ng-enter.ng-enter-active {
      opacity:1;
    }

The key thing to remember here is that, depending on the animation event (which each of the directives above trigger depending on what's going on) two generated CSS classes will be applied to the element; in the example above we have `.ng-enter` and `.ng-enter-active`. For CSS transitions, the transition code must be defined within the starting CSS class (in this case `.ng-enter`). The destination class is what the transition will animate towards.

If for example we wanted to create animations for `leave` and `move` (ngRepeat triggers move) then we can do so using the same CSS naming conventions:

    /* now the element will fade out before it is removed from the DOM */
    .fade.ng-leave {
      transition:0.5s linear all;
      opacity:1;
    }
    .fade.ng-leave.ng-leave-active {
      opacity:0;
    }

We can also make use of CSS Keyframes by referencing the keyframe animation within the starting CSS class:

    /* there is no need to define anything inside of the destination
    CSS class since the keyframe will take charge of the animation */
    .fade.ng-leave {
      animation: my_fade_animation 0.5s linear;
      -webkit-animation: my_fade_animation 0.5s linear;
    }

    @keyframes my_fade_animation {
      from { opacity:1; }
      to { opacity:0; }
    }

    @-webkit-keyframes my_fade_animation {
      from { opacity:1; }
      to { opacity:0; }
    }

Feel free also mix transitions and keyframes together as well as any other CSS classes on the same element.

### CSS Class-based Animations

Class-based animations (animations that are triggered via `ngClass`, `ngShow`, `ngHide` and some other directives) have a slightly different naming convention. Class-based animations are basic enough that a standard transition or keyframe can be referenced on the class being added and removed.

For example if we wanted to do a CSS animation for `ngHide` then we place an animation on the `.ng-hide` CSS class:

    <div ng-show="bool" class="fade">
      Show and hide me
    </div>
    <button ng-click="bool=true">Toggle</button>

    <style>
    .fade.ng-hide {
      transition:0.5s linear all;
      opacity:0;
    }
    </style>

All that is going on here with ngShow/ngHide behind the scenes is the `.ng-hide` class is added/removed (when the hidden state is valid). Since ngShow and ngHide are animation aware then we can match up a transition and ngAnimate handles the rest.

In addition the addition and removal of the CSS class, ngAnimate also provides two helper methods that we can use to further decorate the animation with CSS styles.

    <div ng-class="{on:onOff}" class="highlight">
      Highlight this box
    </div>
    <button ng-click="onOff=!onOff">Toggle</button>

    <style>
    .highlight {
      transition:0.5s linear all;
    }
    .highlight.on-add {
      background:white;
    }
    .highlight.on {
      background:yellow;
    }
    .highlight.on-remove {
      background:black;
    }
    </style>

We can also make use of CSS keyframes by placing them within the CSS classes.

### CSS Staggering Animations

A Staggering animation is a collection of animations that are issued with a slight delay in between each successive operation resulting in a curtain-like effect. The ngAnimate module (versions >=1.2) supports staggering animations and the stagger effect can be performed by creating a ng-EVENT-stagger CSS class and attaching that class to the base CSS class used for the animation. The style property expected within the stagger class can either be a transition-delay or an animation-delay property (or both if your animation contains both transitions and keyframe animations).

    .my-animation.ng-enter {
      /* standard transition code */
      transition: 1s linear all;
      opacity:0;
    }
    .my-animation.ng-enter-stagger {
      /* this will have a 100ms delay between each successive leave animation */
      transition-delay: 0.1s;

      /* in case the stagger doesn't work then the duration value
       must be set to 0 to avoid an accidental CSS inheritance */
      transition-duration: 0s;
    }
    .my-animation.ng-enter.ng-enter-active {
      /* standard transition styles */
      opacity:1;
    }

Staggering animations work by default in ngRepeat (so long as the CSS class is defined). Outside of ngRepeat, to use staggering animations on your own, they can be triggered by firing multiple calls to the same event on $animate. However, the restrictions surrounding this are that each of the elements must have the same CSS className value as well as the same parent element. A stagger operation will also be reset if one or more animation frames have passed since the multiple calls to `$animate` were fired.

The following code will issue the ng-leave-stagger event on the element provided:

    var kids = parent.children();

    $animate.leave(kids[0]); //stagger index=0
    $animate.leave(kids[1]); //stagger index=1
    $animate.leave(kids[2]); //stagger index=2
    $animate.leave(kids[3]); //stagger index=3
    $animate.leave(kids[4]); //stagger index=4

    window.requestAnimationFrame(function() {
      //stagger has reset itself
      $animate.leave(kids[5]); //stagger index=0
      $animate.leave(kids[6]); //stagger index=1

      $scope.$digest();
    });

Stagger animations are currently only supported within CSS-defined animations.

### The `ng-animate` CSS class

When ngAnimate is animating an element it will apply the `ng-animate` CSS class to the element for the duration of the animation. This is a temporary CSS class and it will be removed once the animation is over (for both JavaScript and CSS-based animations).

Therefore, animations can be applied to an element using this temporary class directly via CSS.

    .zipper.ng-animate {
      transition:0.5s linear all;
    }
    .zipper.ng-enter {
      opacity:0;
    }
    .zipper.ng-enter.ng-enter-active {
      opacity:1;
    }
    .zipper.ng-leave {
      opacity:1;
    }
    .zipper.ng-leave.ng-leave-active {
      opacity:0;
    }

(Note that the `ng-animate` CSS class is reserved and it cannot be applied on an element directly since ngAnimate will always remove the CSS class once an animation has completed.)

## JavaScript-based Animations

ngAnimate also allows for animations to be consumed by JavaScript code. The approach is similar to CSS-based animations (where there is a shared CSS class that is referenced in our HTML code) but in addition we need to register the JavaScript animation on the module. By making use of the `module.animation()` module function we can register the ainmation.

Let's see an example of a enter/leave animation using `ngRepeat`:

    <div ng-repeat="item in items" class="slide">
      {{ item }}
    </div>

See the slide CSS class? Let's use that class to define an animation that we'll structure in our module code by using `module.animation`:

    myModule.animation('.slide', [function() {
      return {
        // make note that other events (like addClass/removeClass)
        // have different function input parameters
        enter: function(element, doneFn) {
          jQuery(element).fadeIn(1000, doneFn);

          // remember to call doneFn so that angular
          // knows that the animation has concluded
        },

        move: function(element, doneFn) {
          jQuery(element).fadeIn(1000, doneFn);
        },

        leave: function(element, doneFn) {
          jQuery(element).fadeOut(1000, doneFn);
        }
      }
    }]

The nice thing about JS-based animations is that we can inject other services and make use of advanced animation libraries such as greensock.js and velocity.js.

If our animation code class-based (meaning that something like `ngClass`, `ngHide` and `ngShow` triggers it) then we can still define our animations inside of the same registered animation, however, the function input arguments are a bit different:

    <div ng-class="color" class="colorful">
      this box is moody
    </div>
    <button ng-click="color='red'">Change to red</button>
    <button ng-click="color='blue'">Change to blue</button>
    <button ng-click="color='green'">Change to green</button>

    myModule.animation('.colorful', [function() {
      return {
        addClass: function(element, className, doneFn) {
          // do some cool animation and call the doneFn
        },
        removeClass: function(element, className, doneFn) {
          // do some cool animation and call the doneFn
        },
        setClass: function(element, addedClass, removedClass, doneFn) {
          // do some cool animation and call the doneFn
        }
      }
    }]

## CSS + JS Animations Together

AngularJS 1.4 and higher has taken steps to make the amalgamation of CSS and JS animations more flexible. However, unlike earlier versions of Angular, defining CSS and JS animations to work off of the same CSS class will not work anymore. Therefore the example below will only result in JS animations taking charge of the animation:

    <div ng-if="bool" class="slide">
      Slide in and out
    </div>

    myModule.animation('.slide', [function() {
      return {
        enter: function(element, doneFn) {
          jQuery(element).slideIn(1000, doneFn);
        }
      }
    }]

    .slide.ng-enter {
      transition:0.5s linear all;
      transform:translateY(-100px);
    }
    .slide.ng-enter.ng-enter-active {
      transform:translateY(0);
    }

Does this mean that CSS and JS animations cannot be used together? Do JS-based animations always have higher priority? We can make up for the lack of CSS animations by using the `$animateCss` service to trigger our own tweaked-out, CSS-based animations directly from our own JS-based animation code:

    myModule.animation('.slide', ['$animateCss', function($animateCss) {
      return {
        enter: function(element, doneFn) {
           // this will trigger `.slide.ng-enter` and `.slide.ng-enter-active`.
          var runner = $animateCss(element, {
            event: 'enter',
            structural: true
          }).start();
           runner.done(doneFn);
        }
      }
    }]

The nice thing here is that we can save bandwidth by sticking to our CSS-based animation code and we don't need to rely on a 3rd-party animation framework.

The `$animateCss` service is very powerful since we can feed in all kinds of extra properties that will be evaluated and fed into a CSS transition or keyframe animation. For example if we wanted to animate the height of an element while adding and removing classes then we can do so by providing that data into `$animateCss` directly:

    myModule.animation('.slide', ['$animateCss', function($animateCss) {
      return {
        enter: function(element, doneFn) {
          var runner = $animateCss(element, {
            event: 'enter',
            structural: true,
            addClass: 'maroon-setting',
            from: { height:0 },
            to: { height: 200 }
          }).start();

          runner.done(doneFn);
        }
      }
    }]

Now we can fill in the rest via our transition CSS code:

    /* the transition tells ngAnimate to make the animation happen */
    .slide.ng-enter { transition:0.5s linear all; }

    /* this extra CSS class will be absorbed into the transition
    since the $animateCss code is adding the class */
    .maroon-setting { background:red; }

And `$animateCss` will figure out the rest. Just make sure to have the `done()` callback fire the `doneFn` function to signal when the animation is over.

To learn more about what's possible be sure to visit the $animateCss service.

## Animation Anchoring (via `ng-animate-ref`)

ngAnimate in AngularJS 1.4 comes packed with the ability to cross-animate elements between structural areas of an application (like views) by pairing up elements using an attribute called `ng-animate-ref`.

Let's say for example we have two views that are managed by `ng-view` and we want to show that there is a relationship between two components situated in within these views. By using the `ng-animate-ref` attribute we can identify that the two components are paired together and we can then attach an animation, which is triggered when the view changes.

Say for example we have the following template code:

    <!-- index.html -->
    <div ng-view class="view-animation">
    </div>

    <!-- home.html -->
    <a href="#/banner-page">
      <img src="./banner.jpg" class="banner" ng-animate-ref="banner">
    </a>

    <!-- banner-page.html -->
    <img src="./banner.jpg" class="banner" ng-animate-ref="banner">

Now, when the view changes (once the link is clicked), ngAnimate will examine the HTML contents to see if there is a match reference between any components in the view that is leaving and the view that is entering. It will scan both the view which is being removed (leave) and inserted (enter) to see if there are any paired DOM elements that contain a matching ref value.

The two images match since they share the same ref value. ngAnimate will now create a transport element (which is a clone of the first image element) and it will then attempt to animate to the position of the second image element in the next view. For the animation to work a special CSS class called `ng-anchor` will be added to the transported element.

We can now attach a transition onto the `.banner.ng-anchor` CSS class and then ngAnimate will handle the entire transition for us as well as the addition and removal of any changes of CSS classes between the elements:

    .banner.ng-anchor {
      /* this animation will last for 1 second since there are
             two phases to the animation (an `in` and an `out` phase) */
      transition:0.5s linear all;
    }

We also must include animations for the views that are being entered and removed (otherwise anchoring wouldn't be possible since the new view would be inserted right away).

    .view-animation.ng-enter, .view-animation.ng-leave {
      transition:0.5s linear all;
      position:fixed;
      left:0;
      top:0;
      width:100%;
    }
    .view-animation.ng-enter {
      transform:translateX(100%);
    }
    .view-animation.ng-leave,
    .view-animation.ng-enter.ng-enter-active {
      transform:translateX(0%);
    }
    .view-animation.ng-leave.ng-leave-active {
      transform:translateX(-100%);
    }

Now we can jump back to the anchor animation. When the animation happens, there are two stages that occur: an `out` and an `in` stage. The `out` stage happens first and that is when the element is animated away from its origin. Once that animation is over then the `in` stage occurs which animates the element to its destination. The reason why there are two animations is to give enough time for the enter animation on the new element to be ready.

The example above sets up a transition for both the in and out phases, but we can also target the out or in phases directly via `ng-anchor-out` and `ng-anchor-in`.

    .banner.ng-anchor-out {
      transition: 0.5s linear all;

      /* the scale will be applied during the out animation,
             but will be animated away when the in animation runs */
      transform: scale(1.2);
    }

    .banner.ng-anchor-in {
      transition: 1s linear all;
    }

### Anchoring Demo

Edit in Plunker

    <a href="#/">Home</a>
    <hr />
    <div class="view-container">
      <div ng-view class="view"></div>
    </div>

    angular.module('anchoringExample', ['ngAnimate', 'ngRoute'])
    .config(['$routeProvider', function($routeProvider) {
      $routeProvider.when('/', {
        templateUrl: 'home.html',
        controller: 'HomeController as home'
      });
      $routeProvider.when('/profile/:id', {
        templateUrl: 'profile.html',
        controller: 'ProfileController as profile'
      });
    }])
    .run(['$rootScope', function($rootScope) {
      $rootScope.records = [
        { id:1, title: "Miss Beulah Roob" },
        { id:2, title: "Trent Morissette" },
        { id:3, title: "Miss Ava Pouros" },
        { id:4, title: "Rod Pouros" },
        { id:5, title: "Abdul Rice" },
        { id:6, title: "Laurie Rutherford Sr." },
        { id:7, title: "Nakia McLaughlin" },
        { id:8, title: "Jordon Blanda DVM" },
        { id:9, title: "Rhoda Hand" },
        { id:10, title: "Alexandrea Sauer" }
      ];
    }])
    .controller('HomeController', [function() {
      //empty
    }])
    .controller('ProfileController', ['$rootScope', '$routeParams', function($rootScope, $routeParams) {
      var index = parseInt($routeParams.id, 10);
      var record = $rootScope.records[index - 1];

      this.title = record.title;
      this.id = record.id;
    }]);

    <h2>Welcome to the home page</h1>
    <p>Please click on an element</p>
    <a class="record"
       ng-href="#/profile/{{ record.id }}"
       ng-animate-ref="{{ record.id }}"
       ng-repeat="record in records">
      {{ record.title }}
    </a>

    <div class="profile record" ng-animate-ref="{{ profile.id }}">
      {{ profile.title }}
    </div>

    .record {
      display:block;
      font-size:20px;
    }
    .profile {
      background:black;
      color:white;
      font-size:100px;
    }
    .view-container {
      position:relative;
    }
    .view-container > .view.ng-animate {
      position:absolute;
      top:0;
      left:0;
      width:100%;
      min-height:500px;
    }
    .view.ng-enter, .view.ng-leave,
    .record.ng-anchor {
      transition:0.5s linear all;
    }
    .view.ng-enter {
      transform:translateX(100%);
    }
    .view.ng-enter.ng-enter-active, .view.ng-leave {
      transform:translateX(0%);
    }
    .view.ng-leave.ng-leave-active {
      transform:translateX(-100%);
    }
    .record.ng-anchor-out {
      background:red;
    }

### How is the element transported?

When an anchor animation occurs, ngAnimate will clone the starting element and position it exactly where the starting element is located on screen via absolute positioning. The cloned element will be placed inside of the root element of the application (where ng-app was defined) and all of the CSS classes of the starting element will be applied. The element will then animate into the `out` and `in` animations and will eventually reach the coordinates and match the dimensions of the destination element. During the entire animation a CSS class of `.ng-animate-shim` will be applied to both the starting and destination elements in order to hide them from being visible (the CSS styling for the class is: `visibility:hidden`). Once the anchor reaches its destination then it will be removed and the destination element will become visible since the shim class will be removed.

### How is the morphing handled?

CSS Anchoring relies on transitions and keyframes and the internal code is intelligent enough to figure out what CSS classes differ between the starting element and the destination element. These different CSS classes will be added/removed on the anchor element and a transition will be applied (the transition that is provided in the anchor class). Long story short, ngAnimate will figure out what classes to add and remove which will make the transition of the element as smooth and automatic as possible. Be sure to use simple CSS classes that do not rely on DOM nesting structure so that the anchor element appears the same as the starting element (since the cloned element is placed inside of root element which is likely close to the body element).

Note that if the root element is on the `<html>` element then the cloned node will be placed inside of body.

## Using $animate in your directive code

So far we've explored how to feed in animations into an Angular application, but how do we trigger animations within our own directives in our application? By injecting the `$animate` service into our directive code, we can trigger structural and class-based hooks which can then be consumed by animations. Let's imagine we have a greeting box that shows and hides itself when the data changes

    <greeting-box active="onOrOff">Hi there</greeting-box>

    ngModule.directive('greetingBox', ['$animate', function($animate) {
      return function(scope, element, attrs) {
        attrs.$observe('active', function(value) {
          value ? $animate.addClass(element, 'on') : $animate.removeClass(element, 'on');
        });
      });
    }]);

Now the `on` CSS class is added and removed on the greeting box component. Now if we add a CSS class on top of the greeting box element in our HTML code then we can trigger a CSS or JS animation to happen.

    /* normally we would create a CSS class to reference on the element */
    greeting-box.on { transition:0.5s linear all; background:green; color:white; }

The `$animate` service contains a variety of other methods like `enter`, `leave`, `animate` and `setClass`. To learn more about what's possible be sure to visit the $animate service API page.

### Preventing Collisions With Third Party Libraries

Some third-party frameworks place animation duration defaults across many element or className selectors in order to make their code small and reuseable. This can lead to issues with ngAnimate, which is expecting actual animations on these elements and has to wait for their completion.

You can prevent this unwanted behavior by using a prefix on all your animation classes:

    /* prefixed with animate- */
    .animate-fade-add.animate-fade-add-active {
      transition:1s linear all;
      opacity:0;
    }

You then configure `$animate` to enforce this prefix:

    $animateProvider.classNameFilter(/animate-/);

This also may provide your application with a speed boost since only specific elements containing CSS class prefix will be evaluated for animation when any DOM changes occur in the application.

## Callbacks and Promises

When `$animate` is called it returns a promise that can be used to capture when the animation has ended. Therefore if we were to trigger an animation (within our directive code) then we can continue performing directive and scope related activities after the animation has ended by chaining onto the returned promise that animation method returns.

    // somewhere within the depths of the directive
    $animate.enter(element, parent).then(function() {
      //the animation has completed
    });

(Note that earlier versions of Angular prior to v1.4 required the promise code to be wrapped using `$scope.$apply(...)`. This is not the case anymore.)

In addition to the animation promise, we can also make use of animation-related callbacks within our directives and controller code by registering an event listener using the `$animate` service. Let's say for example that an animation was triggered on our view routing controller to hook into that:

    ngModule.controller('HomePageController', ['$animate', function($animate) {
      $animate.on('enter', ngViewElement, function(element) {
        // the animation for this route has completed
      }]);
    }])

(Note that you will need to trigger a digest within the callback to get angular to notice any scope-related changes.)

## Installation

First include `angular-animate.js` in your HTML:

    <script src="angular.js">
    <script src="angular-animate.js">

You can download this file from the following places:

- Google CDN
  e.g. `//ajax.googleapis.com/ajax/libs/angularjs/X.Y.Z/angular-animate.js`
- Bower
  e.g.

      bower install angular-animate@X.Y.Z

- code.angularjs.org
  e.g.

      "//code.angularjs.org/X.Y.Z/angular-animate.js"

where X.Y.Z is the AngularJS version you are running.

Then load the module in your application by adding it as a dependent module:

    angular.module('app', ['ngAnimate']);

With that you're ready to get started!

## Module Components

### Service

Name | Description
--- | ---
$animateCss | The `$animateCss` service is a useful utility to trigger customized CSS-based transitions/keyframes from a JavaScript-based animation or directly from a directive. The purpose of `$animateCss` is NOT to side-step how `$animate` and ngAnimate work, but the goal is to allow pre-existing animations or directives to create more complex animations that can be purely driven using CSS code.
$animate | The ngAnimate `$animate` service documentation is the same for the core `$animate` service.