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337 lines
16 KiB
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337 lines
16 KiB
Text
@ngdoc overview
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@name Developer Guide: Overview
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@description
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* <a href="#H1_1">What Is Angular?</a>
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* <a href="#H1_3">The Angular Philosophy</a>
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* <a href="#H1_2">Anatomy Of An Angular App</a>
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* <a href="#H1_4">Why You Want Angular</a>
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* <a href="#H1_5">Angular's Ancestors</a>
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* <a href="#H1_6">Watch a Presentation About Angular</a>
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<a name="H1_1"></a>
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# What Is Angular?
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The short answer: angular is a new, powerful, client-side technology that makes it much easier for
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you to create dynamic web sites and complex web apps, all without leaving the comfort of your HTML
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/ JavaScript home.
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The long answer: it kind of depends on where you're coming from...
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* If you're a web designer, you might perceive angular to be a sweet {@link guide.template
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templating} system, that doesn't get in your way and provides you with lots of nice built-ins that
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make it easier to do what you want to do.
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* If you're a web developer, you might be thrilled that angular functions as an excellent web
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framework, one that assists you all the way through the development cycle.
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* If you want to go deeper, you can immerse yourself in angular's extensible HTML {@link
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guide.compiler compiler} that runs in your browser. This compiler teaches your browser new tricks.
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So then, angular's not just a templating system, but you can create fantastic templates with it;
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angular's not just a web framework, but it has a very nice one; and angular's not just an
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extensible HTML compiler, but it has one of those too. Let's put it this way: angular includes
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these parts along with some others; it evolved naturally from earlier occurrences of these forms;
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and thus angular is something far greater than the sum of its parts. It sounds like... it's alive!
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## An Intro By Way of Example
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Let's say that you are a web designer, and you've spent many thous — erm, hundreds of hours
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designing web sites. But at this point, the thought of doing DOM updates, writing listeners, and
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writing input validators, all to do something as simple as implementing a form!? You either don't
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want to go there in the first place or you've been there and the thrill is gone.
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You could even be muttering to yourself as you hack another callback, "This is like building my own
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bike from scratch every time I want to ride to the store." But let's say a clever friend, who keeps
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tabs on these sorts of things, told you to check out angular.
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So now here you are checking out angular, and here is a simple example. Note that it features only
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the templating aspect of angular, but this should suffice for now to quickly demonstrates how much
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easier life can be with angular:
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<doc:example>
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<doc:source>
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<h2>Bigg Bike Shop</h2>
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<hr>
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<b>Invoice:</b>
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<br/>
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<br/>
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<table>
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<tr><td> </td><td> </td>
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<tr><td>Quantity</td><td>Cost</td></tr>
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<tr>
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<td><input name="qty" value="1" ng:validate="integer:0" ng:required/></td>
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<td><input name="cost" value="19.95" ng:validate="number" ng:required/></td>
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</tr>
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</table>
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<hr>
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<b>Total:</b> {{qty * cost | currency}}
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<hr>
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</doc:source>
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<!--
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<doc:scenario>
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it('should show of angular binding', function(){
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expect(binding('qty * cost')).toEqual('$19.95');
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input('qty').enter('2');
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input('cost').enter('5.00');
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expect(binding('qty * cost')).toEqual('$10.00');
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});
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</doc:scenario>
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-->
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</doc:example>
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Go ahead, try out the Live Preview above. "Well I _declare_! It's a fully functioning form, with
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an instantly updating display, and input validation." Speaking of being declarative, let's walk
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through the example and look at the angular-related lines to see what's going on around here.
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In line __2__ of the example, we let the browser know about the angular namespace:
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2 <html xmlns:ng="http://angularjs.org">
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This ensures angular runs nicely in all major browsers.
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In line __3__ we do two angular setup tasks inside a `<script>` tag:
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1. We pull in `angular.js`.
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2. The angular {@link angular.directive.ng:autobind ng:autobind} directive tells angular to {@link
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guide.compiler compile} and manage the whole HTML document.
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3 <script src="file:///Users/krculp/angular.js/build/angular.min.js" ng:autobind></script>
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Lines __14__ and __15__ set up one side of angular's very cool two-way data binding, as well as
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demonstrate some easy input validation:
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14 Quantity: <input name="qty" value="1" ng:validate="integer:0" ng:required/>
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15 Cost: <input name="cost" value="199.95" ng:validate="number" ng:required/>
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These input widgets look normal enough, but consider these points:
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* Remember the `ng:autobind` directive from line 3? When this page loaded, angular bound the names
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of the input widgets (`qty` and `cost`) to variables of the same name. Think of those variables as
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the "Model" part of the Model-View-Controller design pattern.
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* Note the angular directives, {@link angular.widget.@ng:validate ng:validate} and {@link
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ngular.widget.@ng:required ng:required}. You may have noticed that when you enter invalid data or
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leave the the input fields blank, the borders turn a plainly irritated red color, and the display
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value disappears. These `ng:` directives make it easier to implement field validators than coding
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them in JavaScript, no? Yes.
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And finally, the mysterious line #__19__:
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19 Total: {{qty * cost | currency}}
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What's with the curly braces? Those curly braces are your friend. This notation, `{{ _expression_
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}}`, is a bit of built-in angular {@link angular.markup markup}, a shortcut that you use to display
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data. The expression within curly braces gets transformed by the angular compiler into an angular
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directive ({@link angular.directive.ng:bind ng:bind}). The expression itself can be a combination
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of both an expression and a {@link angular.filter filter}: `{{ expression | filter }}`.
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In our example above, we're saying, "Bind the data we got from the input widgets to the display,
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multiply them together, and format the resulting number into something that looks like money."
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<a name="H1_3"></a>
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# The Angular Philosophy
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Angular is built around the belief that declarative code is better than imperative when it comes to
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building UIs and wiring software components together, while imperative code is clearly the way to
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go for expressing business logic.
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Not to put too fine a point on it, but if you wanted to add a new label to your application, you
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could do it by simply adding text to the HTML template, saving the code, and refreshing your
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browser (this here is declarative):
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<pre>
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<span class="label">Hello</span>
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</pre>
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Or, as In programmatic systems (like {@link http://code.google.com/webtoolkit/ GWT}), you would
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have to write the code and then run the code like this:
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<pre>
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var label = new Label();
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label.setText('Hello');
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label.setClass('label');
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parent.addChild(label);
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</pre>
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That looks like, let's see, do some math, factor out the `<pre>`s, carry the one, ummm... a little
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bit of markup versus four times as much code.
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More Angular Philosophy:
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* It is a very good idea to decouple DOM manipulation from app logic. This dramatically improves
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the testability of the code.
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* It is a really, _really_ good idea to regard app testing as equal in importance to app writing.
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Testing difficulty is dramatically affected by the way the code is structured.
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* It is an excellent idea to decouple the client side of an app from the server side. This allows
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development work to progress in parallel, and allows for reuse of both sides.
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* It is very helpful indeed if the framework guides developers through the entire journey of
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building an app: from designing the UI, through writing the business logic, to testing.
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* It is always good to make common tasks trivial and difficult tasks possible.
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Now that we're homing in on what angular is, perhaps now would be a good time to list a few things
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what angular isn't:
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* It's not a Library. You don't just call its functions, although it does provide you with some
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utility APIs.
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* It's not a DOM Manipulation Library. angular uses jQuery to manipulate the DOM behind the scenes,
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rather than give you functions to manipulate the DOM with yourself.
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* It's not a Widget Library. There are lots of existing widget libraries that you can integrate
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with angular.
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* It's not "Just Another Templating System". A part of angular is a templating system. The
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templating subsystem of angular is different from the traditional approach for these reasons:
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* It Uses HTML/CSS syntax: This makes it easy to read and can be edited with existing HTML/CSS
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authoring tools.
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* It Extends HTML vocabulary: Angular allows you to create new HTML tags, which expand into
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dynamic UI components.
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* It Executes in the browser: Removes the round trip to the server for many operations and
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creates instant feedback for users as well as developers.
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* It Has Bidirectional data binding: The model is the single source of truth. Programmatic
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changes to the model are automatically reflected in the view. Any changes by the user to the view
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are automatically reflected in the model.
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<a name="H1_2"></a>
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# Anatomy Of An Angular App
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This section describes the parts of an angular app in more detail.
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## Templates
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{@link guide.template Templates} are the part of angular that makes it easy and fun to create the
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UI for your web apps. With angular's templates you can create a dynamic UI using only HTML and
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CSS, but now you can add your own elements, attributes, and markup. The angular compiler reads the
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"angularized" HTML when your page loads, and follows the instructions in there to generate a
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dynamic page for you. This is the View part of MVC. "But wait there's more": since the compiler is
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extensible, you can build your own declarative language on top of HTML!
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## Application Logic and Behavior
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Application Logic and Behavior, which you define in JavaScript, is the C in MVC. With angular you
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write the logic (the controllers) for your app, but because angular takes care of reflecting the
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state of the model in the view, you don't have to write listeners or DOM manipulators. This feature
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makes your application logic very easy to write, test, maintain, and understand.
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## Data
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In an angular app, all of your data is referenced from inside of a {@link angular.scope scope}.
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The scope is the data Model, the M in the MVC pattern. A scope is a JavaScript object that has
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watcher functions that keep tabs on the data that is referenced from that scope. The data could be
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one or more Javascript objects, arrays, or primitives, it doesn't matter. What matters is that
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these are all referenced by the scope.
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This "scope thing" is how angular takes care of keeping your data model and your UI in sync.
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Whenever something occurs to change the state of the scope, angular immediately reflects that
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change in the UI, and vice versa.
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In addition to the three components described above (the MVC bits), angular comes with a set of
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{@link angular.service Services} that are very helpful for building web apps. The services include
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the following features:
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* You can extend and add application-specific behavior to services.
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* Services include Dependency-Injection, XHR, caching, URL routing, and browser abstraction.
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The following illustration shows the parts of an angular application and how they work together:
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<img class="left" src="img/angular_parts.png" border="0" />
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<a name="H1_4"></a>
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# Why You Want Angular
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Angular frees you from the following pain:
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* **Registering callbacks:** Registering callbacks clutters your code, making it hard to see the
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forest for the trees. Removing common boilerplate code such as callbacks is a good thing. It vastly
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reduces the amount of JavaScript coding _you_ have to do, and it makes it easier to see what your
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application does.
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* **Manipulating HTML DOM programatically:** Manipulating HTML DOM is a cornerstone of AJAX
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applications, but it's cumbersome and error-prone. By declaratively describing how the UI should
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change as your application state changes, you are freed from low level DOM manipulation tasks. Most
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applications written with angular never have to programatically manipulate the DOM, although you
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can if you want to, knock yourself out.
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* **Marshaling data to and from the UI:** CRUD operations make up the majority of AJAX
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applications. The flow of marshaling data from the server to an internal object to an HTML form,
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allowing users to modify the form, validating the form, displaying validation errors, returning to
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an internal model, and then back to the server (gah!) creates a lot of boilerplate code. Angular
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eliminates almost all of this boilerplate, leaving code that describes the overall flow of the
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application rather than all of the implementation details.
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* **Writing tons of initialization code just to get started:** Typically you need to write a lot of
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plumbing just to get a basic "Hello World" AJAX app working. With angular you can bootstrap your
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app easily using services, which are auto-injected into your application in a {@link
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http://code.google.com/p/google-guice/ Guice}-like dependency-injection style. This allows you to
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get started developing features quickly. As a bonus, you get full control over the initialization
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process in automated tests.
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<a name="H1_5"></a>
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# Angular's Ancestors
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Where does angular come from? What events led to the inevitability of the appearance of something
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like angular?
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## First There Was HTML
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HTML was initially designed long, long ago, in the great year of 1989, with the intention to create
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a markup language for sharing scientific documents over the network. Yes, yes, certainly there was
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SGML even before that, but it was so difficult that even esteemed scientists balked at using it.
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Thankfully, Tim Berners-Lee saved all of us from that pain with his much friendlier HTML.
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`<HTML><BODY>Thank You, TB-L!</BODY></HTML>`.
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## Then There Was JavaScript
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Fast forward to 1995: JavaScript was invented. This was done with the best of intentions! But in
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practice it initially served mainly to annoy Internet users with cheap effects that "enhanced"
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static HTML documents.
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Fast forward to the mid 2000s, when a new breed of back-then-considered-rich web applications
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started to appear on the web. These were built with HTML, JavaScript, and CSS, and featured less
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annoying and more impressive effects. Can you recall the first time you saw apps like Gmail, or
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Google Maps, and you couldn't believe everything that was going on in the browser?
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## And JavaScript Prevailed
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As of this writing, in 2011, people are building still richer and more interactive web applications
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that often rival their desktop counterparts. And yet they are essentially still working with
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technology and programming primitives that were used decades ago for the creation of static
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documents with cheap graphic effects. At the same time, the web is HUGE now, and we
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can't just abandon the technologies it was built with. Applets, Flash and Silverlight tried it, and
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in some ways succeeded. Yet many would argue that in reality they failed, because they tried to
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work _around_ the web instead of working _with_ it.
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## And Then There Was Angular
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Angular recognizes the strengths of the existing "static" web technologies, as well as their
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deficiencies. At the same time, angular is learning from the failures of other technologies that
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tried, or are trying, to work around the web.
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For these reasons angular plays to the strengths of established web technologies, instead of
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bypassing them. Angular sets out the goal of increasing the abstraction and programming primitives
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that developers use to build web applications, so as to better reflect the needs of modern web
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applications and their developers.
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<a name="H1_6"></a>
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# Watch a Presentation About Angular
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Here is an early presentation on angular, but note that substantial development has occurred since
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the talk was given in July of 2010.
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<object width="480" height="385">
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<param name="movie" value="http://www.youtube.com/v/elvcgVSynRg&hl=en_US&fs=1"></param>
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<param name="allowFullScreen" value="true"></param>
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<param name="allowscriptaccess" value="always"></param>
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<embed src="http://www.youtube.com/v/elvcgVSynRg&hl=en_US&fs=1"
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type="application/x-shockwave-flash" allowscriptaccess="always"
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allowfullscreen="true" width="480" height="385"></embed>
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</object>
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{@link
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https://docs.google.com/present/edit?id=0Abz6S2TvsDWSZDQ0OWdjaF8yNTRnODczazdmZg&hl=en&authkey=CO-b7oID
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Presentation}
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{@link
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https://docs.google.com/document/edit?id=1ZHVhqC0apbzPRQcgnb1Ye-bAUbNJ-IlFMyPBPCZ2cYU&hl=en&authkey=CInnwLYO
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Source}
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