An introduction to AngularJS
By Steve Ralston | JavaScript, Web Design | Apr 10, 2013:
When I came across AngularJS a couple weeks ago, I was intrigued at first. By the time I had worked through the set of tutorials available on the AngularJS website, I was thrilled to have found this framework.
What is AngularJS? AngularJS is the (relatively) new kid on the coding block. To quote from their website it is “a structural framework for dynamic web apps” which is especially well-suited for building one-page web apps, although it’s certainly not limited to that.
Developed in 2009 by Miško Hevery and Adam Abrons — both Google employees at that time — it is entirely JavaScript and entirely client-side, so anywhere JavaScript can run, AngularJS can run. It’s also small: compressed and minified it’s less than 29 kb. And it’s open source under the MIT license. You can even use the logo, available under the Creative Commons Attribution-ShareAlike 3.0 Unported License.
According to Wikipedia the goal of Angular “is to augment browser-based applications with model–view–controller (MVC) capability” and it does just that, providing a binding/MVC framework. That’s two-way binding, mind you. Delicious. With a structure as simple as {{ my data }}, you bind data to your page. The $scope service detects changes to the model and modifies HTML expressions in the view by way of controllers. Working in the other direction, changes to the view are reflected in the model. This removes the need for the vast majority of data-centric DOM manipulations many of us, myself included, take for granted when working with a library like jQuery.
Angular runs right out of the box with no library dependencies, although it can be extended with the many modules that are available, and of course you can build your own to fit your specific needs. Being pure JavaScript, it also has the benefit of being server-agnostic.
Being accustomed to a powerful library like jQuery, it’s easy to want to mix it in to do things Angular can already do. Recognizing this potential pitfall, the developers have this to say: “If you’re struggling to break the habit, consider removing jQuery from your app. Really. Angular has the $http service and powerful directives that make it almost always unnecessary.” One thing is for sure, if you stick to Angular, the jQuery loops and explicit back-and-forth with the server will be absent from your code, since Angular provides such a succinct and clean method of achieving the same things.
Directives
Angular uses directives to plug its action into the page. Directives, all prefaced with ng-, are placed in html attributes.
Some common directives that come pre-built with Angular are:
ng-app: this is essentially the initial entry point of Angular to the page. It tells Angular where it gets to act. <html ng-app> is all it takes to define a page as an Angular application.
ng-bind: changes the text of an element to the value of an expression.
<span ng:bind=”name”></span> will display the value of ‘name’ inside the span. Any changes to ‘name’ are reflected instantly in the DOM anywhere the variable is used.
<span ng:bind=”name”></span> will display the value of ‘name’ inside the span. Any changes to ‘name’ are reflected instantly in the DOM anywhere the variable is used.
ng-controller: specifies the JavaScript class for the given action. Controllers are typically kept in external .js files.
ng-repeat: creates the very clean loop structures in your page.
<ul> <li ng-repeat="item in items"> {{item.description}} </li> </ul>
effortlessly loops through each item in the collection.
I haven’t used them yet myself, but I have read that creating custom directives can be a tricky issue, something that takes some time to wrap your head around. Angular offers a the concept.
Some sample code
As mentioned before, the ng-app directive in the <html> tag sets the stage for Angular to run in the page.
<html lang="en" ng-app>
Add <script src=”your/path/to/angular/angular.js”></script> to the page head to bring in the Angular framework itself.
<script src=”your/path/to/js/controllers.js”></script> points to the external JavaScript file or files that hold the JavaScript classes your Angular app will call. A very simple class, as an example, might be:
function ItemListCtrl ($scope) { $scope.items = [ { "description": "coffee pot" }, { "description": "nerf gun" }, { "description": "phone" }, ]; }
Passing ng-controller “ItemListCtrl”, the name of my imaginary JavaScript class, tells Angular what code to run:
<body ng-controller="ItemListCtrl">
and double-bracket notation tells Angular what expressions to evaluate.
ng-repeat is a wonderfully succinct repeater directive that loops through the current collection and does the specified action or provides the specified data. It is so simple and clean.
<p>Stuff on my desk:</p> <ul> <li ng-repeat="item in items"> {{item.description}} </li> </ul>
This simple set up will display:
Stuff on my desk: coffee pot nerf gun phone
Admittedly, that doesn’t seem so impressive, but the idea itself is. Very simple page markup and controllers make getting started with Angular, well, very simple.
Getting real data into your app is pleasingly simple too. Angular likes to consume JSON:
function ItemListCtrl ($scope, $http) { $http.get(‘items/list.json').success(function (data) { $scope.items = data; } }
This returns a JSON object that can manipulated at will in your Angular app.
And it’s built for testing, too!
One of the basic tenets Angular was founded on was that apps built with it be fully testable. For end-to-end testing we have Angular Scenario Runner to simulate user interactions with your app. You feed it scenario tests written in JavaScript.
For debugging in the browser, is a Chrome extension available on github.
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