Angular.js Interview Questions and Answers for 10 years experience

1. What is AngularJS and why did you choose it 10 years ago?

   • Answer: AngularJS is a JavaScript-based open-source front-end web application 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. Ten years ago, I chose it because of its MVC architecture, which promoted a clean separation of concerns, making code more maintainable and testable. Its two-way data binding simplified development significantly, and the extensive community support and readily available resources were also major factors.

2. Explain the concept of two-way data binding in AngularJS.

   • Answer: Two-way data binding is a core feature of AngularJS that automatically synchronizes data between the model (data) and the view (UI). Any changes made in the model are instantly reflected in the view, and vice-versa. This eliminates the need for manual DOM manipulation and significantly simplifies the development process. It's achieved through a combination of watchers, digests, and the $apply() cycle.

3. Describe the different scopes in AngularJS.

   • Answer: AngularJS uses a hierarchical scope system. The root scope is created at the application's initialization. Child scopes are created for directives, controllers, and other components. Scopes facilitate data sharing between controllers and views. Changes in a child scope don't automatically affect its parent scope unless explicitly designed that way. This hierarchical structure helps isolate components and prevents unintended side effects.

4. What are directives in AngularJS? Give examples.

   • Answer: Directives extend HTML by adding new attributes, elements, or CSS classes. They allow you to create reusable UI components. Examples include `ng-model` (for two-way data binding), `ng-repeat` (for iterating over arrays), `ng-if` (for conditional rendering), and `ng-switch` (for conditional switching between templates). Custom directives can also be created to encapsulate complex UI logic and behavior.

5. Explain the concept of services in AngularJS.

   • Answer: Services are singleton objects used to share data and functionality across multiple controllers and components. They help achieve modularity, improve code reusability, and promote testability. They are typically created using the `factory`, `service`, `provider`, or `constant` methods, each having slightly different behaviors and lifecycles. They often interact with external resources, such as APIs or databases.

6. How do you handle routing in AngularJS?

   • Answer: AngularJS uses the `ngRoute` module (or other third-party routing solutions) to handle routing. It allows you to define different routes, each mapping to a specific view (template) and controller. The `$routeProvider` configures routes and associates them with controllers. The `$location` service manages the URL in the browser address bar.

7. Explain the difference between `$scope.$watch` and `$scope.$apply`.

   • Answer: `$scope.$watch` registers a listener function that gets executed whenever a specific scope property changes. `$scope.$apply` is used to trigger the digest cycle, updating the view based on any model changes that occurred outside the AngularJS context (e.g., due to a user interaction with a non-AngularJS element or a timer). `$apply` is crucial for ensuring consistency between the model and the view.

8. What are AngularJS filters? Give examples.

   • Answer: Filters format data for display in the view. Examples include `currency`, `date`, `filter`, `json`, `lowercase`, `number`, `orderBy`, and `uppercase`. Custom filters can also be created for application-specific formatting needs. They take data as input and return the formatted data.

9. How do you handle AJAX calls in AngularJS?

   • Answer: AngularJS provides the `$http` service for making AJAX calls. It's used to send HTTP requests (GET, POST, PUT, DELETE, etc.) to servers and handles the responses. It supports promises, allowing for asynchronous operations and error handling. The response data is then integrated into the AngularJS model.

10. Explain dependency injection in AngularJS.

    • Answer: Dependency injection is a design pattern where dependencies are provided to a component rather than being created within the component itself. AngularJS uses constructor injection, where dependencies are passed as arguments to a controller's or service's constructor. This improves testability and promotes modularity. It allows easy swapping of dependencies during testing.

11. How do you test AngularJS applications?

    • Answer: AngularJS applications can be tested using various approaches, including unit tests (testing individual components in isolation), integration tests (testing the interaction between multiple components), and end-to-end tests (testing the entire application flow). Frameworks like Karma and Jasmine are commonly used for unit testing, while Protractor can be used for end-to-end testing. Mocking is also essential for testing interactions with external resources.

12. What are some common performance issues in AngularJS applications and how do you address them?

    • Answer: Common performance issues include slow digest cycles (due to excessive watchers), inefficient DOM manipulation, and large data sets. Solutions include optimizing watchers (using one-time bindings or simplifying expressions), using techniques like memoization to reduce repetitive calculations, optimizing the use of ng-repeat (e.g., using track by), and using pagination or virtualization for large datasets. Profiling tools can help identify bottlenecks.

13. Describe your experience working with AngularJS in large-scale projects.

    • Answer: [This answer will be highly project-specific and should detail the scale of the projects, the challenges faced (e.g., managing large teams, maintaining code consistency, scaling performance), and the solutions implemented. Mention any specific architecture patterns used, such as using states, services, and factories effectively to compartmentalize application logic and state. Highlight successful strategies for collaboration and maintainability.]

14. How do you handle error handling in AngularJS?

    • Answer: Error handling is typically done using `try...catch` blocks within controllers and services. For HTTP requests using `$http`, the `then()` and `catch()` methods of promises are used to handle successful responses and errors respectively. Custom error handling services or interceptors can be implemented to centralize error reporting and logging. User-friendly error messages should be presented to the user.

15. What are some best practices for writing clean and maintainable AngularJS code?

    • Answer: Best practices include using a consistent coding style, adhering to the MVC pattern, using meaningful names for variables and functions, writing modular code (using services, factories and directives), keeping controllers and views concise, writing thorough unit tests, and using version control (like Git).

16. Explain the difference between a controller and a service in AngularJS.

    • Answer: Controllers are responsible for managing the logic and data associated with a specific view. Services are reusable components that perform tasks and can be injected into controllers and other services. Controllers are typically tied to a specific scope, while services are singletons, creating only one instance per application.

17. How do you secure an AngularJS application?

    • Answer: Security in AngularJS involves several aspects: input validation to prevent XSS (cross-site scripting) attacks, using HTTPS for secure communication, properly authenticating users (using token-based authentication or OAuth), and protecting sensitive data (using appropriate encryption and secure storage techniques). Regularly updating dependencies is also crucial.

18. What are some alternatives to AngularJS and why would you choose them over AngularJS?

    • Answer: Alternatives include Angular (Angular 2+), React, Vue.js, and others. The choice depends on the project's needs and preferences. Angular (Angular 2+) offers improved performance and architecture, React offers a component-based approach with virtual DOM for efficient updates, while Vue.js provides a more gradual learning curve and simpler integration. AngularJS is now considered legacy and lacks the performance and feature improvements offered by newer frameworks.

19. Describe a challenging AngularJS project you worked on and how you overcame the challenges.

    • Answer: [This answer should describe a specific project, highlighting the challenges encountered (e.g., tight deadlines, complex requirements, performance bottlenecks, legacy code). Focus on the specific steps taken to overcome those challenges and the positive results. Quantify the results whenever possible (e.g., improved performance by X%, reduced development time by Y%).]

20. Explain your understanding of the digest cycle in AngularJS.

    • Answer: The digest cycle is AngularJS's mechanism for detecting changes in the model and updating the view accordingly. It iterates through all the watchers registered on the scopes, checking for changes in their values. If changes are detected, the corresponding parts of the view are updated. The cycle continues until no more changes are detected. It's crucial for the two-way data binding.

21. How do you optimize AngularJS applications for mobile devices?

    • Answer: Optimizing for mobile involves minimizing the amount of JavaScript code (using minification and code splitting), optimizing images, using a responsive design, and minimizing HTTP requests. Consider using tools that help to improve the mobile experience, including progressive web app (PWA) technology. Testing on different mobile devices is crucial to identify and address any platform-specific issues.

22. What are promises in AngularJS and how are they used?

    • Answer: Promises are used to handle asynchronous operations (like AJAX calls). They represent the eventual result of an asynchronous operation. They have three states: pending, fulfilled, and rejected. Methods such as `.then()` and `.catch()` are used to handle the different states of a promise, allowing for asynchronous programming that's cleaner and more manageable than callbacks.

23. Explain your experience with AngularJS testing frameworks like Karma and Jasmine.

    • Answer: [This answer should describe the experience using these frameworks, including examples of test types created, the approaches to testing different parts of the application, and strategies for maintaining a comprehensive test suite. Mention any specific techniques used to improve testing efficiency or coverage.]

24. How do you handle internationalization (i18n) in AngularJS?

    • Answer: Internationalization involves adapting the application to different languages and regions. In AngularJS, this can be achieved using filters, services to manage locale-specific data, and libraries that help with translating text and formatting dates, numbers, and currencies according to the user's locale. Separating text from code and storing it in language files is a common practice.

25. What are some common anti-patterns to avoid in AngularJS development?

    • Answer: Common anti-patterns include overusing watchers, creating overly complex controllers, neglecting error handling, improper use of scopes (especially with broadcast/emit), and not following a consistent coding style. Avoid creating too many nested scopes. Ensure proper use of services for separating concerns and reusability.

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