AngularJS is a great JavaScript framework that comes with some very compelling features, not just for developers but for designers too! In this tutorial, we’ll cover what I consider to be the most important features and how they can help your next web application become even better.

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Elevator Pitch: Introduction to AngularJS

AngularJS is a new, powerful client-side technology that provides a way to accomplish really powerful things in a way that embraces and extends HTML, CSS, and JavaScript, while making up for some of its obvious Defects. If HTML was built for dynamic content, this would be it.

In this article, we will introduce some of the most important AngularJS concepts to understand the "big picture". My goal is that after seeing some of these features, you'll be excited to build some fun stuff with AngularJS.

Function 1: Two-way data binding

Think of your model as the single source of truth for your application. You can read or update anything in your application in a model.

Data binding is probably the coolest and most useful feature in AngularJS. It will save you from writing a lot of boilerplate code. A typical web application may contain as much as 80% of its code base dedicated to traversing, manipulating, and listening to the DOM. Data binding makes this code disappear so you can focus on your application.

Think of your model as the single source of truth for your application. You can read or update anything in your application in a model. Data binding directives provide the projection of the model onto the application view. This projection is seamless and requires no effort on your part.

Traditionally, when models change, developers are responsible for manually manipulating DOM elements and attributes to reflect those changes. This is a two-way street. On the one hand, changes in the model drive changes in DOM elements. On the other hand, changes to DOM elements require changes to the model. User interactions complicate the situation further, as developers are responsible for interpreting interactions, incorporating them into models, and updating views. This is a very manual and tedious process that becomes difficult to control as the size and complexity of the application increases.

There must be a better way! AngularJS's two-way data binding handles synchronization between the DOM and the model and vice versa.

This is a simple example showing how to bind an input value to a

  
  
    
      
    

    
      

        Name:
        
        

        
Hello, {{yourName}}!
      
    
  

This is so easy to set up and almost magical...

Function 2: Template

It's important to realize that AngularJS never operates on templates as strings. This is all browser DOM.

In AngularJS, templates are just plain old HTML. The HTML vocabulary has been expanded to include instructions on how to project models into views.

The browser parses the HTML template into DOM. The DOM will then become the input to the AngularJS compiler. AngularJS traverses the DOM template to render directives, which are called directives. Collectively, these directives are responsible for setting up data bindings for your application views.

It's important to realize that AngularJS never operates on templates as strings. The input to AngularJS is the browser DOM, not an HTML string. Data binding is a DOM transformation, not a string concatenation or innerHTML change. Using DOM as input, instead of strings, is the biggest difference between AngularJS and its brother frameworks. Using the DOM lets you expand your directive vocabulary and build your own directives, even abstracting them into reusable components!

One of the biggest advantages of this approach is that it creates a tight workflow between designers and developers. Designers can mark up HTML as normal, and developers can then easily take over the baton and hook functionality via bindings.

Here is an example where I use the ng-repeat directive to loop through an images array and fill it with what is essentially an img template.

function AlbumCtrl($scope) {
	scope.images = [
		{"thumbnail":"img/image_01.png", "description":"Image 01 description"},
		{"thumbnail":"img/image_02.png", "description":"Image 02 description"},
		{"thumbnail":"img/image_03.png", "description":"Image 03 description"},
		{"thumbnail":"img/image_04.png", "description":"Image 04 description"},
		{"thumbnail":"img/image_05.png", "description":"Image 05 description"}
	];
}

As a side note, it's also worth mentioning that AngularJS doesn't force you to learn new syntax or pull templates from your application.

Feature 3: MVC

AngularJS incorporates the fundamental principles behind the original MVC software design pattern into the way client-side web applications are built.

MVC or Model-View-Controller pattern means a lot of different things to different people. AngularJS does not implement MVC in the traditional sense, but is closer to MVVM (Model-View-ViewModel).

模型

模型只是应用程序中的数据。 模型只是普通的旧 JavaScript 对象。无需从框架类继承、将其包装在代理对象中或使用特殊的 getter/setter 方法来访问它。事实上，我们正在处理普通的 JavaScript，这是一个非常好的功能，它减少了应用程序的样板。

视图模型

视图模型是一个提供特定数据和方法来维护特定视图的对象。

viewmodel 是位于 AngularJS 应用程序中的 $scope 对象。 $scope 只是一个简单的 JavaScript 对象，带有一个小型 API，旨在检测和广播其状态的更改。

控制器

控制器负责设置初始状态并使用控制行为的方法增强 $scope。值得注意的是，控制器不存储状态，也不与远程服务交互。

视图

视图是 AngularJS 解析并编译 HTML 以包含呈现的标记和绑定后存在的 HTML。

该部门为构建您的应用程序奠定了坚实的基础。 $scope 具有对数据的引用，控制器 定义行为，视图 处理布局并将交互移交给控制器 > 做出相应的回应。

功能4：依赖注入

AngularJS 有一个内置的依赖注入子系统，可以帮助开发人员使应用程序更易于开发、理解和测试。

依赖注入（DI）允许您请求依赖项，而不必去寻找它们或自己创建它们。将其视为“嘿，我需要 X”的一种方式，DI 负责为您创建和提供它。

要访问核心 AngularJS 服务，只需将该服务添加为参数即可； AngularJS 将检测到您需要该服务并为您提供一个实例。

  function EditCtrl($scope, $location, $routeParams) {
       // Something clever here...
  }

您还可以定义自己的自定义服务并使这些服务也可用于注入。

  angular.
      module('MyServiceModule', []).
      factory('notify', ['$window', function (win) {
      return function (msg) {
          win.alert(msg);
      };
  }]);

  function myController(scope, notifyService) {
      scope.callNotify = function (msg) {
          notifyService(msg);
      };
  }

  myController.$inject = ['$scope', 'notify'];

功能 5：指令

指令是我个人最喜欢的 AngularJS 功能。您是否曾经希望您的浏览器能够为您带来新的功能？好吧，现在可以了！这是 AngularJS 我最喜欢的部分之一。这也可能是 AngularJS 最具挑战性的方面。

指令可用于创建用作新的自定义小部件的自定义 HTML 标记。它们还可以用于用行为“装饰”元素并以有趣的方式操作 DOM 属性。

这是一个简单的指令示例，该指令侦听事件并相应地更新其 $scope。

  myModule.directive('myComponent', function(mySharedService) {
      return {
          restrict: 'E',
          controller: function($scope, $attrs, mySharedService) {
              $scope.$on('handleBroadcast', function() {
                  $scope.message = 'Directive: ' + mySharedService.message;
              });
          },
          replace: true,
          template: ''
      };
  });

然后，您可以像这样使用这个自定义指令。

将应用程序创建为离散组件的组合，可以非常轻松地根据需要添加、更新或删除功能。

奖励功能：测试

AngularJS 团队强烈认为任何用 JavaScript 编写的代码都需要进行一组强大的测试。他们在设计 AngularJS 时考虑到了可测试性，因此可以尽可能轻松地测试您的 AngularJS 应用程序。所以没有理由不这样做。

鉴于 JavaScript 是动态的、解释性的，而不是编译性的，对于开发人员来说，在编写测试时采用严格的思维方式非常重要。

AngularJS 完全是从头开始编写的，可测试。它甚至配备了端到端和单元测试运行程序设置。如果您想查看实际效果，请查看 Angular-seed 项目：https://github.com/angular/angular-seed。

一旦有了种子项目，对其进行测试就轻而易举了。输出如下所示：

API 文档充满了端到端测试，这些测试在说明框架的某个部分应该如何工作方面做了令人难以置信的工作。一段时间后，我发现自己直接进行测试以了解某些内容是如何工作的，然后可能会阅读其余的文档来找出答案。

结论

我们已经介绍了我喜欢的 AngularJS 众多功能中的六个。我相信这六个功能不仅对于启动和运行 AngularJS 至关重要，而且对于以可维护和可扩展的方式将应用程序组合在一起也是至关重要的。

AngularJS 的网站 http://angularjs.org 有大量的工作示例和大量优秀的文档。我还建议您查看 AngularJS 邮件列表上的精彩社区。​​p>

让我知道你的想法！