Top Angular Interview Questions

Question: What is Angular and what are its key features?

Answer:

Angular is a platform and framework for building single-page client applications using HTML and TypeScript. Developed and maintained by Google, Angular allows developers to build dynamic, modern web applications by extending HTML’s capabilities with built-in directives, services, and tools. Angular is known for its robustness, scalability, and developer-friendly features, making it a popular choice for building large-scale enterprise applications.

Key Features of Angular:

1. Component-Based Architecture:

   • Angular applications are built using components, which encapsulate the HTML, CSS, and logic related to a specific part of the application. This promotes reusability and modularity.

2. Two-Way Data Binding:

   • Angular allows for synchronization between the model and the view. When the model changes, the view reflects the change automatically, and when the user interacts with the view, the model is updated accordingly. This reduces the need for manual DOM manipulation.

3. Dependency Injection:

   • Angular provides a powerful dependency injection (DI) system, which allows services and other components to be injected into other components and services. This promotes testability, modularity, and reduces the need for tightly-coupled code.

4. Directives:

   • Directives are special markers attached to elements in the DOM that extend HTML’s capabilities. Angular provides built-in directives like ngIf, ngFor, etc., which allow for conditional rendering, looping, and other dynamic behaviors.

5. Routing:

   • Angular provides a powerful routing module to handle navigation within single-page applications. It supports features like lazy loading, route guards, and nested routing, making navigation seamless and efficient.

6. RxJS and Reactive Programming:

   • Angular uses RxJS, a library for reactive programming, which allows developers to work with asynchronous data streams in a more declarative and efficient manner. RxJS integrates with Angular’s change detection and event handling system, making it ideal for handling complex asynchronous operations.

7. Angular CLI:

   • The Angular Command Line Interface (CLI) is a powerful tool that helps in automating common tasks like project creation, development, testing, and deployment. It simplifies the development workflow and enhances productivity.

8. Angular Forms:

   • Angular provides two types of forms: Template-driven forms and Reactive forms. Both approaches allow for easy data collection and validation, providing flexibility depending on the complexity of the form.

9. Cross-Platform Development:

   • Angular supports building applications that can run on different platforms like web, mobile, and desktop. Angular can be combined with frameworks like Ionic to build mobile applications and Electron for desktop applications.

10. Internationalization (i18n):

    • Angular offers tools for internationalizing applications, allowing developers to build applications that can be easily translated into different languages.

11. Ahead-of-Time (AOT) Compilation:

    • Angular uses AOT compilation, which compiles the application during build time rather than runtime. This results in faster application startup, smaller bundle sizes, and better performance.

Angular’s ecosystem is rich with tools and libraries that support the entire development lifecycle, from designing user interfaces to testing, optimizing performance, and managing the build and deployment process.

Question: What is the difference between AngularJS and Angular (2+ versions)?

Answer:

AngularJS and Angular (2+ versions) are both web application frameworks developed by Google, but there are significant differences between them in terms of architecture, features, and overall approach to development. AngularJS is the original version (also referred to as Angular 1.x), while Angular (2 and above) is a complete rewrite of the framework. Here’s a detailed comparison:

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1. Architecture:

• AngularJS:
  • AngularJS follows the Model-View-Controller (MVC) or Model-View-ViewModel (MVVM) architecture. The application is structured around controllers and directives.
  • It uses two-way data binding to synchronize data between the model and the view, making it simpler but sometimes performance-heavy for large applications.
• Angular (2+):
  • Angular 2+ follows a Component-based architecture. In this approach, everything in the application is structured as components, which encapsulate the logic, view (HTML), and styling (CSS) together.
  • This architecture promotes better modularity, scalability, and reusability. It is also easier to manage state and lifecycle hooks in a component-based system.

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2. Language:

• AngularJS:
  • AngularJS is written in JavaScript and uses JavaScript for the entire development.
• Angular (2+):
  • Angular uses TypeScript, a superset of JavaScript that provides features like static typing, interfaces, and modern JavaScript (ES6/ES7) support. TypeScript helps catch errors during development, making code more robust and easier to maintain.

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3. Performance:

• AngularJS:
  • AngularJS relies on two-way data binding, which can lead to performance issues, especially in large applications. When the model changes, AngularJS has to update the view, and vice versa, which can cause inefficient digest cycles and slow down the application.
• Angular (2+):
  • Angular improves performance by using unidirectional data flow and change detection strategies (such as OnPush). It also leverages Ahead-of-Time (AOT) compilation and Tree Shaking, which reduces the size of the app and improves performance.
  • Angular 2+ also has lazy loading for modules, which improves load times by loading only the necessary parts of the application initially.

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4. Dependency Injection:

• AngularJS:
  • AngularJS provides a basic dependency injection (DI) system, but it can be less flexible and harder to manage for larger applications.
• Angular (2+):
  • Angular 2+ offers a more powerful and flexible dependency injection system. It allows for better scope management, hierarchies, and providers, making the system more maintainable and scalable, especially in complex applications.

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5. Routing:

• AngularJS:
  • AngularJS uses the ngRoute module for routing, but it is less feature-rich and flexible.
• Angular (2+):
  • Angular uses the Angular Router, which is much more powerful and flexible. It supports features like lazy loading, nested routes, route guards, parameterized routes, and preloading strategies. This makes it more suitable for large-scale, complex applications.

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6. Mobile Support:

• AngularJS:
  • AngularJS does not have built-in support for mobile development, making it less optimal for building mobile-first applications.
• Angular (2+):
  • Angular is optimized for mobile development. It supports mobile-friendly features like responsive layouts and can be combined with frameworks like Ionic to build cross-platform mobile applications.

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7. Tooling and Ecosystem:

• AngularJS:
  • The tooling in AngularJS is somewhat limited compared to Angular 2+. It has basic support for building, testing, and deploying, but it lacks some of the advanced features found in modern frameworks.
• Angular (2+):
  • Angular comes with an advanced set of tools, particularly the Angular CLI (Command Line Interface). The CLI makes tasks like project creation, build, testing, and deployment much easier and faster. The tooling is more integrated and has strong support for development, including unit testing, end-to-end testing, and linting.

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8. Mobile and Desktop Support:

• AngularJS:
  • AngularJS doesn’t have built-in mobile and desktop application support, and additional frameworks are often needed for mobile development.
• Angular (2+):
  • Angular is more capable of building cross-platform applications. With the integration of frameworks like Ionic (for mobile) and Electron (for desktop), developers can create mobile and desktop apps using Angular.

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9. Backward Compatibility:

• AngularJS:
  • AngularJS applications are not directly compatible with Angular 2+. Since Angular 2+ is a complete rewrite, upgrading from AngularJS to Angular 2+ requires significant changes in the codebase.
• Angular (2+):
  • Angular 2+ does not support AngularJS applications natively. Migrating from AngularJS to Angular 2+ requires a refactor of the entire application, but Angular provides tools like ngUpgrade to facilitate the migration process.

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10. Learning Curve:

• AngularJS:
  • AngularJS is generally easier to learn for developers who are already familiar with JavaScript since it doesn’t require knowledge of TypeScript or the new concepts introduced in Angular 2+.
• Angular (2+):
  • Angular 2+ has a steeper learning curve due to its more complex features like TypeScript, RxJS, Angular CLI, and dependency injection. However, the new architecture and features make it much more suitable for large-scale, maintainable applications.

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Summary of Key Differences:

Feature	AngularJS (1.x)	Angular (2+)
Language	JavaScript	TypeScript
Architecture	MVC/MVVM	Component-based
Data Binding	Two-way binding	Unidirectional data flow
Performance	Less efficient for large apps	Optimized with AOT, Tree shaking, and lazy loading
Dependency Injection	Basic	Advanced and flexible
Routing	ngRoute module	Angular Router with advanced features
Mobile Support	Limited	Optimized for mobile and desktop support
Tooling	Basic	Angular CLI and advanced tools
Backward Compatibility	N/A	No direct compatibility with AngularJS
Learning Curve	Easier for JS developers	Steeper due to new concepts

In summary, Angular (2+) is a more modern, performant, and flexible framework that leverages TypeScript, component-based architecture, and a powerful set of tools for building scalable, maintainable applications. AngularJS is the older version that lacks many of the advanced features introduced in Angular 2+. As Angular continues to evolve, AngularJS is considered legacy, and new projects are recommended to use Angular 2+ or later.

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