concepts.html

<h1><code ng:non-bindable=""></code>
<span class="hint"></span>
</h1>
<div><h2>Overview</h2>

<p>This document gives a quick overview of the main angular components and how they work together.
These are:</p>

<ul>
<li><a href="guide/concepts#startup">startup</a> - bring up hello world</li>
<li><a href="guide/concepts#runtime">runtime</a> - overview of angular runtime</li>
<li><a href="guide/concepts#scope">scope</a> - the glue between the view and the controller</li>
<li><a href="guide/concepts#controller">controller</a> - application behavior</li>
<li><a href="guide/concepts#model">model</a> - your application data</li>
<li><a href="guide/concepts#view">view</a> - what the user sees</li>
<li><a href="guide/concepts#directives">directives</a> - extend HTML vocabulary</li>
<li><a href="guide/concepts#filters">filters</a> - format the data in user locale</li>
<li><a href="guide/concepts#injector">injector</a> - assembles your application</li>
<li><a href="guide/concepts#module">module</a> - configures the injector</li>
<li><a href="guide/concepts#angular_namespace"><code>$</code></a> - angular namespace</li>
</ul>

<p><a name="startup"></a></p>

<h2>Startup</h2>

<p>This is how we get the ball rolling (refer to the diagram and example below):</p>

<p><img class="pull-right" style="padding-left: 3em;" src="img/guide/concepts-startup.png"></p>

<ol>
<li>Browser loads the HTML and parses it into a DOM</li>
<li>Browser loads <code>angular.js</code> script</li>
<li>Angular waits for <code>DOMContentLoaded</code> event</li>
<li>Angular looks for <a href="api/ng.directive:ngApp"><code>ng-app</code></a>
<a href="guide/directive">directive</a>, which designates application boundary</li>
<li><a href="guide/module">Module</a> specified in <a href="api/ng.directive:ngApp"><code>ng-app</code></a> (if any) is used to configure
 the <a href="api/AUTO.$injector"><code>$injector</code></a></li>
<li><a href="api/AUTO.$injector"><code>$injector</code></a> is used to create the <a href="api/ng.$compile"><code>$compile</code></a> service as well as <a href="api/ng.$rootScope"><code>$rootScope</code></a></li>
<li><a href="api/ng.$compile"><code>$compile</code></a> service is used to compile the DOM and link
 it   with <a href="api/ng.$rootScope"><code>$rootScope</code></a></li>
<li><a href="api/ng.directive:ngInit"><code>ng-init</code></a> <a href="guide/directive">directive</a> assigns <code>World</code> to the <code>name</code> property on the <a href="guide/scope">scope</a></li>
<li>The <code>{{name}}</code> <a href="api/ng.$interpolate"><code>interpolates</code></a> the expression to
 <code>Hello World!</code></li>
</ol>

<div class="clear">
</div>

<h3>Source</h3>
<div source-edit="" source-edit-deps="angular.js" source-edit-html="index.html-17" source-edit-css="" source-edit-js="" source-edit-unit="" source-edit-scenario=""></div>
<div class="tabbable"><div class="tab-pane" title="index.html">
<pre class="prettyprint linenums" ng-set-text="index.html-17" ng-html-wrap=" angular.js"></pre>
<script type="text/ng-template" id="index.html-17">
    <p ng-init=" name='World' ">Hello {{name}}!</p>
  </script>
</div>
</div><h3>Demo</h3>
<div class="well doc-example-live" ng-embed-app="" ng-set-html="index.html-17" ng-eval-javascript=""></div>

<p><a name="runtime"></a></p>

<h2>Runtime</h2>

<p><img class="pull-right" style="padding-left: 3em; padding-bottom: 1em;" src="img/guide/concepts-runtime.png"></p>

<p>The diagram and the example below describe how Angular interacts with browser's event loop.</p>

<ol>
<li>Browsers event-loop waits for an event to arrive. Event is a user interactions, timer event,
 or network event (response from a server).</li>
<li>The events callback gets executed. This enters the JavaScript context. The callback can
  modify the DOM structure.</li>
<li>Once the callback finishes execution, the browser leaves the JavaScript context and
 re-renders the view based on DOM changes.</li>
</ol>

<p>Angular modifies the normal JavaScript flow by providing it's own event processing loop. This
splits the JavaScript into classical and Angular execution context. Only operations which are
applied in Angular execution context will benefit from angular data-binding, exception handling,
property watching, etc... Use $apply() to enter Angular execution context from JavaScript. Keep in
mind that in most places (controllers, services) the $apply has already been called for you by the
directive which is handling the event. The need to call $apply is reserved only when
implementing custom event callbacks, or when working with a third-party library callbacks.</p>

<ol>
<li>Enter Angular execution context by calling <a href="guide/scope">scope</a><code>.</code><a href="api/ng.$rootScope.Scope#$apply"><code>$apply</code></a><code>(stimulusFn)</code>. Where <code>stimulusFn</code> is
 the work you wish to do in Angular execution context.</li>
<li>Angular executes the <code>stimulusFn()</code>, which typically modifies application state.</li>
<li>Angular enters the <a href="api/ng.$rootScope.Scope#$digest"><code>$digest</code></a> loop. The
 loop is made up of two smaller loops which process <a href="api/ng.$rootScope.Scope#$evalAsync"><code>$evalAsync</code></a> queue and the <a href="api/ng.$rootScope.Scope#$watch"><code>$watch</code></a> list. The <a href="api/ng.$rootScope.Scope#$digest"><code>$digest</code></a> loop keeps iterating until the model
 stabilizes, which means that the <a href="api/ng.$rootScope.Scope#$evalAsync"><code>$evalAsync</code></a> queue is empty and the <a href="api/ng.$rootScope.Scope#$watch"><code>$watch</code></a> list does not detect any changes.</li>
<li>The <a href="api/ng.$rootScope.Scope#$evalAsync"><code>$evalAsync</code></a> queue is used to
 schedule work which needs to occur outside of current stack frame, but before the browser
 view render. This is usually done with <code>setTimeout(0)</code>, but the <code>setTimeout(0)</code> approach
 suffers from slowness and may cause view flickering since the browser renders the view after
 each event.</li>
<li>The <a href="api/ng.$rootScope.Scope#$watch"><code>$watch</code></a> list is a set of expressions
 which may have changed since last iteration. If a change is detected then the <code>$watch</code>
 function is called which typically updates the DOM with the new value.</li>
<li>Once Angular <a href="api/ng.$rootScope.Scope#$digest"><code>$digest</code></a> loop finishes
 the execution leaves the Angular and JavaScript context. This is followed by the browser
 re-rendering the DOM to reflect any changes.</li>
</ol>

<p>Here is the explanation of how the <code>Hello wold</code> example achieves the data-binding effect when the
user enters text into the text field.</p>

<ol>
<li>During the compilation phase:
<ol><li>the <a href="api/ng.directive:ngModel"><code>ng-model</code></a> and <a href="api/ng.directive:input"><code>input</code></a> <a href="guide/directive">directive</a> set up a <code>keydown</code> listener on the <code>&lt;input&gt;</code> control.</li>
<li>the <a href="api/ng.$interpolate"><code>&#123;&#123;name&#125;&#125;</code></a> interpolation
sets up a <a href="api/ng.$rootScope.Scope#$watch"><code>$watch</code></a> to be notified of
<code>name</code> changes.</li></ol></li>
<li>During the runtime phase:
<ol><li>Pressing an '<code>X</code>' key causes the browser to emit a <code>keydown</code> event on the input control.</li>
<li>The <a href="api/ng.directive:input"><code>input</code></a> directive
captures the change to the input's value and calls <a href="api/ng.$rootScope.Scope#$apply"><code>$apply</code></a><code>("name = 'X';")</code> to update the
application model inside the Angular execution context.</li>
<li>Angular applies the <code>name = 'X';</code> to the model.</li>
<li>The <a href="api/ng.$rootScope.Scope#$digest"><code>$digest</code></a> loop begins</li>
<li>The <a href="api/ng.$rootScope.Scope#$watch"><code>$watch</code></a> list detects a change
on the <code>name</code> property and notifies the <a href="api/ng.$interpolate"><code>&#123;&#123;name&#125;&#125;</code></a> interpolation, which in turn updates the DOM.</li>
<li>Angular exits the execution context, which in turn exits the <code>keydown</code> event and with it
the JavaScript execution context.</li>
<li>The browser re-renders the view with update text.</li></ol></li>
</ol>

<div class="clear">
</div>

<h3>Source</h3>
<div source-edit="" source-edit-deps="angular.js" source-edit-html="index.html-18" source-edit-css="" source-edit-js="" source-edit-unit="" source-edit-scenario=""></div>
<div class="tabbable"><div class="tab-pane" title="index.html">
<pre class="prettyprint linenums" ng-set-text="index.html-18" ng-html-wrap=" angular.js"></pre>
<script type="text/ng-template" id="index.html-18">
    <input ng-model="name">
    <p>Hello {{name}}!</p>
  </script>
</div>
</div><h3>Demo</h3>
<div class="well doc-example-live" ng-embed-app="" ng-set-html="index.html-18" ng-eval-javascript=""></div>

<p><a name="scope"></a></p>

<h2>Scope</h2>

<p>The <a href="guide/scope">scope</a> is responsible for detecting changes to the model section and
provides the execution context for expressions. The scopes are nested in a hierarchical structure
which closely follow the DOM structure. (See individual directive documentation to see which
directives cause a creation of new scopes.)</p>

<p>The following example demonstrates how <code>name</code> <a href="guide/expression">expression</a> will evaluate
into different value depending on which scope it is evaluated in. The example is followed by
a diagram depicting the scope boundaries.</p>

<div class="clear">
</div>

<div class="show-scope">
<h3>Source</h3>
<div source-edit="" source-edit-deps="angular.js script.js" source-edit-html="index.html-19" source-edit-css="style.css-21" source-edit-js="script.js-20" source-edit-unit="" source-edit-scenario=""></div>
<div class="tabbable"><div class="tab-pane" title="index.html">
<pre class="prettyprint linenums" ng-set-text="index.html-19" ng-html-wrap=" angular.js script.js"></pre>
<script type="text/ng-template" id="index.html-19">
    <div ng-controller="GreetCtrl">
      Hello {{name}}!
    </div>
    <div ng-controller="ListCtrl">
      <ol>
        <li ng-repeat="name in names">{{name}}</li>
      </ol>
    </div>
  </script>
</div>
<div class="tab-pane" title="style.css">
<pre class="prettyprint linenums" ng-set-text="style.css-21"></pre>
<style type="text/css" id="style.css-21">
    .show-scope .doc-example-live.ng-scope,
    .show-scope .doc-example-live .ng-scope  {
      border: 1px solid red;
      margin: 3px;
    }
  </style>
</div>
<div class="tab-pane" title="script.js">
<pre class="prettyprint linenums" ng-set-text="script.js-20"></pre>
<script type="text/ng-template" id="script.js-20">
    function GreetCtrl($scope) {
      $scope.name = 'World';
    }

    function ListCtrl($scope) {
      $scope.names = ['Igor', 'Misko', 'Vojta'];
    }
  </script>
</div>
</div><h3>Demo</h3>
<div class="well doc-example-live" ng-embed-app="" ng-set-html="index.html-19" ng-eval-javascript="script.js-20"></div>
</div>

<p><img class="center" src="img/guide/concepts-scope.png"></p>

<p><a name="controller"></a></p>

<h2>Controller</h2>

<p><img class="pull-right" style="padding-left: 3em; padding-bottom: 1em;" src="img/guide/concepts-controller.png"></p>

<p>Controller is the code behind the view. Its job is to construct the model and publish it to the
view along with callback methods. The view is a projection of the scope onto the template (the
HTML). The scope is the glue which marshals the model to the view and forwards the events to the
controller.</p>

<p>The separation of the controller and the view is important because:</p>

<ul>
<li>The controller is written in JavaScript. JavaScript is imperative. Imperative is a good fit
for specifying application behavior. The controller should not contain any rendering
information (DOM references or HTML fragments).</li>
<li>The view template is written in HTML. HTML is declarative. Declarative is a good fit for
specifying UI. The View should not contain any behavior.</li>
<li>Since the controller is unaware of the view, there could be many views for the same
controller. This is important for re-skinning, device specific views (i.e. mobile vs desktop),
and testability.</li>
</ul>

<div class="clear">
</div>

<h3>Source</h3>
<div source-edit="" source-edit-deps="angular.js script.js" source-edit-html="index.html-22" source-edit-css="" source-edit-js="script.js-23" source-edit-unit="" source-edit-scenario=""></div>
<div class="tabbable"><div class="tab-pane" title="index.html">
<pre class="prettyprint linenums" ng-set-text="index.html-22" ng-html-wrap=" angular.js script.js"></pre>
<script type="text/ng-template" id="index.html-22">
    <div ng-controller="MyCtrl">
      Hello {{name}}!
      <button ng-click="action()">
        OK
      </button>
    </div>
  </script>
</div>
<div class="tab-pane" title="script.js">
<pre class="prettyprint linenums" ng-set-text="script.js-23"></pre>
<script type="text/ng-template" id="script.js-23">
    function MyCtrl($scope) {
      $scope.action = function() {
        $scope.name = 'OK';
      }

      $scope.name = 'World';
    }
  </script>
</div>
</div><h3>Demo</h3>
<div class="well doc-example-live" ng-embed-app="" ng-set-html="index.html-22" ng-eval-javascript="script.js-23"></div>

<p><a name="model"></a></p>

<h2>Model</h2>

<p><img class="pull-right" style="padding-left: 3em; padding-bottom: 1em;" src="img/guide/concepts-model.png"></p>

<p>The model is the data which is used merged with the template to produce the view. To be able to
render the model into the view, the model has to be referenceable from the scope. Unlike many
other frameworks Angular makes no restrictions or requirements an the model. There are no classes
to inherit from or special accessor methods for accessing or changing the model. The model can be
primitive, object hash, or a full object Type. In short the model is a plain JavaScript object.</p>

<div class="clear">
</div>

<p><a name="view"></a></p>

<h2>View</h2>

<p><img class="pull-right" style="padding-left: 3em; padding-bottom: 1em;" src="img/guide/concepts-view.png"></p>

<p>The view is what the users sees. The view begins its life as a template, it is merged with the
model and finally rendered into the browser DOM. Angular takes a very different approach to
rendering the view, to most other templating systems.</p>

<ul>
<li><strong>Others</strong> - Most templating systems begin as an HTML string with special templating markup.
Often the template markup breaks the HTML syntax which means that the template can not be
edited by an HTML editor. The template string is then parsed by the template engine, and
merged with the data. The result of the merge is an HTML string. The HTML string is then
written to the browser using the <code>.innerHTML</code>, which causes the browser to render the HTML.
When the model changes the whole process needs to be repeated. The granularity of the template
is the granularity of the DOM updates. The key here is that the templating system manipulates
strings.</li>
<li><strong>Angular</strong> - Angular is different, since its templating system works on DOM objects not on
strings. The template is still written in HTML string, but it is HTML (not HTML with
template sprinkled in.) The browser parses the HTML into DOM, and the DOM becomes the input to
the template engine know as the <a href="api/ng.$compile"><code>compiler</code></a>. The compiler
looks for <a href="guide/directive">directives</a> which in turn set up <a href="api/ng.$rootScope.Scope#$watch"><code>watches</code></a> on the model. The result is a
continuously updating view which does not need template model re-merging. Your model becomes
the single source-of-truth for your view.</li>
</ul>

<div class="clear">
</div>

<h3>Source</h3>
<div source-edit="" source-edit-deps="angular.js" source-edit-html="index.html-24" source-edit-css="" source-edit-js="" source-edit-unit="" source-edit-scenario=""></div>
<div class="tabbable"><div class="tab-pane" title="index.html">
<pre class="prettyprint linenums" ng-set-text="index.html-24" ng-html-wrap=" angular.js"></pre>
<script type="text/ng-template" id="index.html-24">
    <div ng-init="list = ['Chrome', 'Safari', 'Firefox', 'IE'] ">
      <input ng-model="list" ng-list> <br>
      <input ng-model="list" ng-list> <br>
      <pre>list={{list}}</pre> <br>
      <ol>
        <li ng-repeat="item in list">
          {{item}}
        </li>
      </ol>
    </div>
  </script>
</div>
</div><h3>Demo</h3>
<div class="well doc-example-live" ng-embed-app="" ng-set-html="index.html-24" ng-eval-javascript=""></div>

<p><a name="directives"></a></p>

<h2>Directives</h2>

<p>A directive is a behavior or DOM transformation which is triggered by a presence of an attribute,
element name, or a class name. A directive allows you to extend the HTML vocabulary in a
declarative fashion. Following is an example which enables data-binding for the <code>contenteditable</code>
in HTML.</p>

<h3>Source</h3>
<div source-edit="directive" source-edit-deps="angular.js script.js" source-edit-html="index.html-26" source-edit-css="style.css-27" source-edit-js="script.js-25" source-edit-unit="" source-edit-scenario=""></div>
<div class="tabbable"><div class="tab-pane" title="index.html">
<pre class="prettyprint linenums" ng-set-text="index.html-26" ng-html-wrap="directive angular.js script.js"></pre>
<script type="text/ng-template" id="index.html-26">
    <div contentEditable="true" ng-model="content">Edit Me</div>
    <pre>model = {{content}}</pre>
  </script>
</div>
<div class="tab-pane" title="style.css">
<pre class="prettyprint linenums" ng-set-text="style.css-27"></pre>
<style type="text/css" id="style.css-27">
    div[contentEditable] {
      cursor: pointer;
      background-color: #D0D0D0;
      margin-bottom: 1em;
      padding: 1em;
    }
  </style>
</div>
<div class="tab-pane" title="script.js">
<pre class="prettyprint linenums" ng-set-text="script.js-25"></pre>
<script type="text/ng-template" id="script.js-25">
    angular.module('directive', []).directive('contenteditable', function() {
      return {
        require: 'ngModel',
        link: function(scope, elm, attrs, ctrl) {
          // view -> model
          elm.bind('blur', function() {
            scope.$apply(function() {
              ctrl.$setViewValue(elm.html());
            });
          });

          // model -> view
          ctrl.render = function(value) {
            elm.html(value);
          };

          // load init value from DOM
          ctrl.$setViewValue(elm.html());
        }
      };
    });
  </script>
</div>
</div><h3>Demo</h3>
<div class="well doc-example-live" ng-embed-app="directive" ng-set-html="index.html-26" ng-eval-javascript="script.js-25"></div>

<p><a name="filters"></a></p>

<h2>Filters</h2>

<p><a href="api/ng.$filter"><code>Filters</code></a> perform data transformation roles. Typically
they are used in conjunction with the locale to format the data in locale specific output.
They follow the spirit of UNIX filters and use similar syntax <code>|</code> (pipe).</p>

<h3>Source</h3>
<div source-edit="" source-edit-deps="angular.js" source-edit-html="index.html-28" source-edit-css="" source-edit-js="" source-edit-unit="" source-edit-scenario=""></div>
<div class="tabbable"><div class="tab-pane" title="index.html">
<pre class="prettyprint linenums" ng-set-text="index.html-28" ng-html-wrap=" angular.js"></pre>
<script type="text/ng-template" id="index.html-28">
    <div ng-init="list = ['Chrome', 'Safari', 'Firefox', 'IE'] ">
      Number formatting: {{ 1234567890 | number }} <br>
      array filtering <input ng-model="predicate">
      {{ list | filter:predicate | json }}
    </div>
  </script>
</div>
</div><h3>Demo</h3>
<div class="well doc-example-live" ng-embed-app="" ng-set-html="index.html-28" ng-eval-javascript=""></div>

<p><a name="module"></a>
<a name="injector"></a></p>

<h2>Modules and the Injector</h2>

<p><img class="pull-right" style="padding-left: 3em; padding-bottom: 1em;" src="img/guide/concepts-module-injector.png"></p>

<p>An <a href="api/AUTO.$injector"><code>injector</code></a> is a service locator. There is a single
<a href="api/AUTO.$injector"><code>injector</code></a> per Angular <a href="api/ng.directive:ngApp"><code>application</code></a>. The <a href="api/AUTO.$injector"><code>injector</code></a> provides a way to look up an object instance by its
name. The injector keeps an internal cache of all objects so that repeated calls to get the same
object name result in the same instance. If the object does not exist, then the <a href="api/AUTO.$injector"><code>injector</code></a> asks the instance factory to create a new instance.</p>

<p>A <a href="api/angular.Module"><code>module</code></a> is a way to configure the injector's instance factory, known
as a <a href="api/AUTO.$provide"><code>provider</code></a>.</p>

<div class='clear'>
</div>

<pre class="prettyprint linenums">
  // Create a module
  var myModule = angular.module('myModule', [])

  // Configure the injector
  myModule.factory('serviceA', function() {
    return {
      // instead of {}, put your object creation here
    };
  });

  // create an injector and configure it from 'myModule'
  var $injector = angular.injector(['myModule']);

  // retrieve an object from the injector by name
  var serviceA = $injector.get('serviceA');

  // always true because of instance cache
  $injector.get('serviceA') === $injector.get('serviceA');
</pre>

<p>But the real magic of the <a href="api/AUTO.$injector"><code>injector</code></a> is that it can be
used to <a href="api/AUTO.$injector#invoke"><code>call</code></a> methods and <a href="api/AUTO.$injector#instantiate"><code>instantiate</code></a> types. This subtle feature is what
allows the methods and types to ask for their dependencies instead of having to look for them.</p>

<pre class="prettyprint linenums">
  // You write functions such as this one.
  function doSomething(serviceA, serviceB) {
    // do something here.
  }

  // Angular provides the injector for your application
  var $injector = ...;

  ///////////////////////////////////////////////
  // the old-school way of getting dependencies.
  var serviceA = $injector.get('serviceA');
  var serviceB = $injector.get('serviceB');

  // now call the function
  doSomething(serviceA, serviceB);

  ///////////////////////////////////////////////
  // the cool way of getting dependencies.
  // the $injector will supply the arguments to the function automatically
  $injector.invoke(doSomething); // This is how the framework calls your functions
</pre>

<p>Notice that the only thing you needed to write was the function, and list the dependencies in the
function arguments. When angular calls the function, it will use the <a href="api/AUTO.$injector#invoke"><code>call</code></a> which will automatically fill the function
arguments.</p>

<p>Examine the <code>ClockCtrl</code> bellow, and notice how it lists the dependencies in the constructor. When the
<a href="api/ng.directive:ngController"><code>ng-controller</code></a> instantiates
the controller it automatically provides the dependencies. There is no need to create
dependencies, look for dependencies, or even get a reference to the injector.</p>

<h3>Source</h3>
<div source-edit="timeExampleModule" source-edit-deps="angular.js script.js" source-edit-html="index.html-29" source-edit-css="" source-edit-js="script.js-30" source-edit-unit="" source-edit-scenario=""></div>
<div class="tabbable"><div class="tab-pane" title="index.html">
<pre class="prettyprint linenums" ng-set-text="index.html-29" ng-html-wrap="timeExampleModule angular.js script.js"></pre>
<script type="text/ng-template" id="index.html-29">
    <div ng-controller="ClockCtrl">
      Current time is: {{ time.now }}
    </div>
  </script>
</div>
<div class="tab-pane" title="script.js">
<pre class="prettyprint linenums" ng-set-text="script.js-30"></pre>
<script type="text/ng-template" id="script.js-30">
    angular.module('timeExampleModule', []).
      // Declare new object call time,
      // which will be available for injection
      factory('time', function($timeout) {
        var time = {};

        (function tick() {
          time.now = new Date().toString();
          $timeout(tick, 1000);
        })();
        return time;
      });

    // Notice that you can simply ask for time
    // and it will be provided. No need to look for it.
    function ClockCtrl($scope, time) {
      $scope.time = time;
    }
  </script>
</div>
</div><h3>Demo</h3>
<div class="well doc-example-live" ng-embed-app="timeExampleModule" ng-set-html="index.html-29" ng-eval-javascript="script.js-30"></div>

<p><a name="angular_namespace"></a></p>

<h2>Angular Namespace</h2>

<p>To prevent accidental name collision, Angular prefixes names of objects which could potentially
collide with <code>$</code>. Please do not use the <code>$</code> prefix in your code as it may accidentally collide
with Angular code.</p></div>