AngularJS is the frontend part of the MEAN stack, consisting of MongoDB database, Express.js web application server framework, Angular.js itself, and Node.js server runtime environment.
AngularJS is a structural framework for dynamic web applications. It lets you use HTML as your template language and lets you extend HTML’s syntax to express your application components clearly and succinctly. Its data binding and dependency injection eliminate much of the code you currently have to write. And, it all happens within the browser, making it an ideal partner with any server technology.