AngularJS and Angular 2+ (commonly referred to as just "Angular") are two distinct versions of the Angular framework, and there are significant differences between them.

Here are some of the key distinctions:

1. Architecture:

   • AngularJS: AngularJS is based on the Model-View-Controller (MVC) architecture. In AngularJS, the controller manages the application's logic, and two-way data binding synchronizes the model and view.

   • Angular 2+: Angular has a component-based architecture. It uses a hierarchy of components, each with its own template, logic, and styles. It promotes a more modular and structured approach to building applications.

2. Language:

   • AngularJS: AngularJS is primarily written in JavaScript.

   • Angular 2+: Angular is written in TypeScript, a statically typed superset of JavaScript. TypeScript provides strong typing, which helps catch errors at compile time and enhances code maintainability.

3. Performance:

   • AngularJS: AngularJS can suffer from performance issues with large and complex applications due to its two-way data binding and digest cycle.

   • Angular 2+: Angular is designed with performance in mind. It uses a unidirectional data flow and a more efficient change detection mechanism, making it more suitable for large-scale applications.

4. Directives:

   • AngularJS: AngularJs uses directives extensively to extend HTML's functionality and create custom behaviors.

   • Angular 2+: While Angular still uses directives, their usage and syntax have changed significantly. Directives in Angular are more focused on manipulating the DOM and attaching behaviors to elements.

5. Dependency Injection:

   • AngularJS: AngularJS has a basic dependency injection system, but it's not as robust as the one in Angular.

   • Angular 2+: Angular features a powerful and hierarchical dependency injection system that makes it easier to manage dependencies and perform unit testing.

6. Component-Based vs. Controller-Based:

   • AngularJS: AngularJS primarily uses controllers and scopes to manage application logic and data binding.

   • Angular 2+: Angular adopts a component-based architecture, where components are the building blocks of an application. Each component encapsulates its own logic, template, and styles.

7. Mobile Development:

   • AngularJS: While AngularJS can be used for mobile development, it wasn't specifically designed for mobile applications.

   • Angular 2+: Angular has a separate framework called "Angular for Mobile," which is optimized for building mobile applications.

8. Tooling:

   • AngularJS: AngularJS had limited tooling support compared to Angular.

   • Angular 2+: Angular has a rich ecosystem of tools and libraries, including the Angular CLI (Command-Line Interface), which simplifies project setup, development, testing, and deployment.

9. Backward Compatibility:

   • AngularJS: AngularJS applications might require significant changes when migrating to newer versions of Angular.

   • Angular 2+: Angular provides migration tools and guides, but transitioning from AngularJS to Angular can still be a complex process.

In summary, Angular 2+ introduced many improvements over AngularJS, such as better performance, a component-based architecture, TypeScript support, and a more robust dependency injection system. However, migrating from AngularJS to Angular may require careful planning and effort due to the fundamental differences between the two versions.