AngularJS

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AngularJS
AngularJS logo
Developer(s) Brat Tech LLC, Google and community.
Initial release 2009 (2009)
Stable release 1.3.15 / March 17, 2015; 42 days ago (2015-03-17)
Development status Active
Written in JavaScript
Platform Cross-platform, see Legacy browser support
Size 123 KiB production
938 KiB development
Type JavaScript library
License MIT License
Website angularjs.org

In software development, AngularJS (commonly referred to as "Angular") is an open-source web application framework maintained by Google and by a community of individual developers and corporations to address many of the challenges encountered in developing single-page applications. It aims to simplify both the development and the testing of such applications by providing a framework for client-side model–view–controller (MVC) architecture, along with components commonly used in rich Internet applications.

The AngularJS library works by first reading the HTML page, which has embedded into it additional custom tag attributes. Angular interprets those attributes as directives to bind input or output parts of the page to a model that is represented by standard JavaScript variables. The values of those JavaScript variables can be manually set within the code, or retrieved from static or dynamic JSON resources.

Philosophy[edit]

AngularJS is built around the belief that declarative programming should be used for building user interfaces and connecting software components, while imperative programming is better suited to defining an application's business logic.[1] The framework adapts and extends traditional HTML to present dynamic content through two-way data-binding that allows for the automatic synchronization of models and views. As a result, AngularJS de-emphasizes DOM manipulation with the goal of improving testability and performance.

AngularJS's design goals include:

  • Decouple DOM manipulation from application logic. This difficulty is dramatically affected by the way the code is structured.
  • Decouple the client side of an application from the server side. This allows development work to progress in parallel, and allows for reuse of both sides.
  • Provide structure for the journey of building an application: from designing the UI, through writing the business logic, to testing.

Angular implements the MVC pattern to separate presentation, data, and logic components. Using dependency injection, Angular brings traditionally server-side services, such as view-dependent controllers, to client-side web applications. Consequently, much of the burden on the server can be reduced.

Scope[edit]

Angular uses the term "Scope" to mean something different than what it usually means in computer science.

Scope in computer science describes when in the program a particular binding is in effect. The ECMA-262 specification defines scope as a lexical environment that defines the environment in which a Function object is executed[2] in a similar way as scope is defined in lambda calculus[3]

In Angular, "scope" is a certain kind of object[4] that itself can be in scope or out of scope in any given part of the program, following the usual rules of variable scope in JavaScript like any other object.[5] When the term "scope" is used below, it means the Angular scope object and not the variable scope.

Bootstrapper[edit]

The tasks performed by the AngularJS bootstrapper occur in three phases[6] after the DOM has been loaded:

  1. Creation of a new Injector
  2. Compilation of the directives that decorate the DOM
  3. Linking of all directives to scope

AngularJS directives allow the developer to specify custom and reusable HTML-like elements and attributes that define data bindings and the behavior of presentation components. Some of the most commonly used directives are:

ng-app
Declares the root element of an AngularJS application, under which directives can be used to declare bindings and define behavior.
ng-bind
Sets the text of a DOM element to the value of an expression. For example, <span ng-bind="name"></span> will display the value of ‘name’ inside the span element. Any changes to the variable ‘name’ in the application's scope are reflected instantly in the DOM.
ng-model
Similar to ng-bind, but establishes a two-way data binding between the view and the scope.
ng-model-options
Allows tuning how model updates are done.
ng-class
Allows class attributes to be dynamically loaded.
ng-controller
Specifies a JavaScript controller class that evaluates HTML expressions.
ng-repeat
Instantiate an element once per item from a collection.
ng-show & ng-hide
Conditionally show or hide an element, depending on the value of a boolean expression. Show and hide is achieved by setting the CSS display style.
ng-switch
Conditionally instantiate one template from a set of choices, depending on the value of a selection expression.
ng-view
The base directive responsible for handling routes that resolve JSON before rendering templates driven by specified controllers.
ng-if
Basic if statement directive that allow to show the following element if the conditions are true. When the condition is false, the element is removed from the DOM. When true, a clone of the compiled element is re-inserted
ng-aria
A module for accessibility support of common ARIA attributes.
ng-animate
A module provides support for JavaScript, CSS3 transition and CSS3 keyframe animation hooks within existing core and custom directives..

Two-way data binding[edit]

AngularJS' two-way data binding is its most notable feature, and it reduces the amount of code written[citation needed] by relieving the server backend of templating responsibilities. Instead, templates are rendered in plain HTML according to data contained in a scope defined in the model. The $scope service in Angular detects changes to the model section and modifies HTML expressions in the view via a controller. Likewise, any alterations to the view are reflected in the model. This circumvents the need to actively manipulate the DOM and encourages bootstrapping and rapid prototyping of web applications.[7] AngularJS detects changes in models by comparing the current values with values stored earlier in a process of dirty-checking, unlike Ember.js and Backbone.js that trigger listeners when the model values are changed.[8]

Chrome plugin[edit]

In July 2012, the Angular team built a plugin for the Google Chrome browser called Batarang,[9] that improves the debugging experience for web applications built with Angular. The extension aims to allow for easy detection of performance bottlenecks and offers a GUI for debugging applications.[10] The extension is not compatible with recent releases (after v1.2.x) of Angular.[11]

Development history[edit]

AngularJS was originally developed in 2009 by Miško Hevery and Adam Abrons[12] at Brat Tech LLC[13] as the software behind an online JSON storage service, that would have been priced by the megabyte, for easy-to-make applications for the enterprise. This venture was located at the web domain "GetAngular.com",[13] and had a few subscribers, before the two decided to abandon the business idea and release Angular as an open-source library.[citation needed]

Abrons left the project, but Hevery, who works at Google, continues to develop and maintain the library with fellow Google employees Igor Minár and Vojta Jína.[14]

Releases[edit]

As of March 17, 2015, release 1.3.15 (code name locality-filtration) is the current stable version and 1.4.0-rc.0 (code name Sartorial Chronography) is the current unstable beta release available since April 10, 2015.

The code names are super-power related, composed of two hyphen-joined words, should sound “fun / crazy / cool”, and are publicly submitted and voted by users.[15]

Legacy browser support[edit]

Versions 1.2 and later of AngularJS do not support Internet Explorer versions 6 or 7.[16] Versions 1.3 and later of AngularJS dropped support for Internet Explorer 8.[17]

Comparisons to Backbone.js[edit]

Data-binding
The most prominent feature that separates the two libraries is in the way models and views are synchronized. Whereas AngularJS supports two way data-binding, Backbone.js relies heavily on boilerplate code to harmonize its models and views.[18]
REST
Backbone.js communicates well with RESTful backends. A very simple use of REST APIs is also available with AngularJS using the $resource service. AngularJS also provides a $http service that is more flexible, connecting to remote servers either through a browser's XMLHttpRequest object or via JSONP.
Templating
AngularJS templating uses a combination of customizable HTML tags and expressions. Backbone.js ships with underscore.js's utility function template() and also integrates with different templating engines such as Mustache.[18]

References[edit]

  1. ^ "What Is Angular?". Retrieved 12 February 2013. 
  2. ^ "Annotated ECMAScript 5.1, Section 10.2 Lexical Environments". Retrieved 2015-01-03. 
  3. ^ Barendregt, Henk; Barendsen, Erik (March 2000), Introduction to Lambda Calculus (PDF) 
  4. ^ "AngularJS: Developer Guide: Scopes". Retrieved 2015-01-03. 
  5. ^ "ECMA-262-3 in detail. Chapter 4. Scope chain.". Retrieved 2015-01-03. 
  6. ^ "Writing Directives". angularjs.org. November 28, 2012. Retrieved 2013-07-21. 
  7. ^ "5 Awesome AngularJS Features". Retrieved 13 February 2013. 
  8. ^ Misko Hevery. "Databinding in angularjs". Retrieved 2014-03-09. 
  9. ^ "angular/angularjs-batarang (GitHub)". Retrieved 2014-10-12. 
  10. ^ Ford, Brian. "Introducing the AngularJS Batarang". AngularJS Blog. Retrieved 2014-10-12. 
  11. ^ "batarang Chrome extension for AngularJS appears broken". 
  12. ^ "Hello World, <angular/> is here". Retrieved 2014-10-12. 
  13. ^ a b "GetAngular". Angular / BRAT Tech. LLC. Retrieved 2014-10-12. 
  14. ^ "Contributors to angular/angular.js (GitHub)". Retrieved 2014-10-12. 
  15. ^ "AngularJS Code Names - Google Moderator". Google. Retrieved 2014-10-12. 
  16. ^ "AngularJS: Developer Guide: Internet Explorer Compatibility". Google. Retrieved 2014-10-12. 
  17. ^ Minar, Igor. "AngularJS 1.3: a new release approaches". AngularJS Blog. Retrieved 2014-10-12. 
  18. ^ a b "Backbonejs vs Angularjs: Demystifying the myths". Retrieved 13 February 2013. 

Further reading[edit]

See also[edit]

External links[edit]