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 AngularJS is a JavaScript-based open-source front-end web framework mainly maintained by Google and by a community of individuals 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) and model–view–ViewModel (MVVM) architectures, along with components commonly used in rich Internet applications.

AngularJS is used as the frontend of the MEAN stack, consisting of MongoDB database, Express.js web application server framework, Angular.js itself, and Node.js server runtime environment. Version 1.8.x is on Long Term Support until December 31st, 2021. After that date, Google will no longer update AngularJS and Angular (2.0+) is suggested instead.[3][4]

The AngularJS framework works by first reading the Hypertext Markup Language (HTML) page, which has additional custom HTML attributes embedded into it. 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.

AngularJS is built on the belief that declarative programming should be used to create user interfaces and connect software components, while imperative programming is better suited to defining an application's business logic.[5] 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 explicit Document Object Model (DOM) manipulation with the goal of improving testability and performance.

AngularJS's design goals include:

to decouple DOM manipulation from application logic. The difficulty of this is dramatically affected by the way the code is structured.

to decouple the client side of an application from the server-side. This allows development work to progress in parallel and allows for the reuse of both sides.

to provide structure for the journey of building an application: from designing the UI, through writing the business logic, to testing.

AngularJS implements the MVC pattern to separate presentation, data, and logic components.[6] 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.

AngularJS uses the term "scope" in a manner akin to the fundamentals of computer science.

Scope in computer science describes when in the program a particular binding is valid. The ECMA-262 specification defines scope as a lexical environment in which a Function object is executed in client-side web scripts;[7] akin to how scope is defined in lambda calculus.[8]

As a part of the "MVC" architecture, the scope forms the "Model", and all variables defined in the scope can be accessed by the "View" as well as the "Controller". The scope behaves as a glue and binds the "View" and the "Controller".