Angular.js Interview Questions and Answers

1. What is AngularJS?

   • Answer: AngularJS is a structural framework for dynamic web apps. It lets you use HTML as your template language and extends HTML's syntax to express your application's components clearly and succinctly. It's 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.

2. What are the key features of AngularJS?

   • Answer: Key features include Model-View-Controller (MVC) architecture, two-way data binding, dependency injection, directives, templating, routing, and testing capabilities.

3. Explain the Model-View-Controller (MVC) architecture in AngularJS.

   • Answer: MVC separates an application into three interconnected parts: Model (data), View (UI), and Controller (logic). The Model holds the data, the View displays the data, and the Controller handles user interactions and updates both the Model and the View.

4. What is two-way data binding in AngularJS?

   • Answer: Two-way data binding automatically synchronizes data between the Model and the View. Any changes made in the Model are reflected in the View, and vice-versa. This simplifies development and reduces boilerplate code.

5. 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. This promotes modularity, testability, and reusability.

6. What are directives in AngularJS? Give examples.

   • Answer: Directives extend HTML with new attributes, elements, and CSS classes. Examples include `ng-model`, `ng-repeat`, `ng-bind`, `ng-if`, and custom directives.

7. What is the purpose of the `ng-model` directive?

   • Answer: `ng-model` creates a two-way data binding between the UI element and a scope variable. Changes in the UI update the variable, and changes in the variable update the UI.

8. What is the `ng-repeat` directive used for?

   • Answer: `ng-repeat` iterates over a collection (array or object) and dynamically creates a template for each item in the collection.

9. Explain the difference between `ng-bind` and `{{}}` interpolation.

   • Answer: Both `ng-bind` and `{{}}` display data from the scope, but `ng-bind` is generally preferred for performance reasons because it avoids flickering (initial display of the expression before the data is bound).

10. What are AngularJS scopes?

    • Answer: Scopes are objects that act as bridges between the Model and the View. They hold the data and provide a way for controllers and directives to access and manipulate data.

11. What is the role of a controller in AngularJS?

    • Answer: Controllers act as the glue between the Model and the View. They handle user interactions, update the Model, and manage the data displayed in the View.

12. Explain AngularJS services.

    • Answer: Services are singleton objects that provide functionality to controllers and other parts of the application. They are useful for encapsulating reusable logic, such as data access or communication with external APIs.

13. How do you create a custom service in AngularJS?

    • Answer: You create a custom service using the `$provide` service or by defining a factory or service function.

14. What are filters in AngularJS? Give examples.

    • Answer: Filters format data displayed in the View. Examples include `date`, `currency`, `lowercase`, `uppercase`, `number`, and custom filters.

15. How do you create a custom filter in AngularJS?

    • Answer: You create a custom filter by registering a function with the `$filterProvider` service.

16. Explain AngularJS routing.

    • Answer: Routing allows you to create single-page applications with multiple views. It maps URLs to different parts of your application, so users can navigate between views without full page reloads.

17. What is the `$routeProvider` service used for?

    • Answer: The `$routeProvider` is used to configure routes in AngularJS applications. You define routes by specifying URLs and the corresponding controllers and views.

18. What are the different ways to handle events in AngularJS?

    • Answer: You can handle events using directives like `ng-click`, `ng-submit`, `ng-change`, or by using event listeners within controllers or directives.

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

    • Answer: `$scope.$watch` monitors a scope variable for changes, while `$scope.$apply` updates the scope after asynchronous operations (like AJAX calls).

20. What are promises in AngularJS?

    • Answer: Promises are used to handle asynchronous operations, making code cleaner and easier to read. They represent the eventual result of an asynchronous operation.

21. How do you use $http service in AngularJS?

    • Answer: The `$http` service is used to make AJAX requests (GET, POST, PUT, DELETE, etc.) to servers.

22. What is a factory in AngularJS?

    • Answer: A factory is a function that returns an object containing the service's methods and properties. It offers more flexibility than a service definition.

23. What is a service in AngularJS?

    • Answer: A service is a constructor function that is instantiated using `new` keyword. It's often used when you need to manage the service's state.

24. What is the difference between a factory and a service in AngularJS?

    • Answer: Factories return objects, while services are constructor functions. Factories offer more flexibility in terms of what they return.

25. Explain AngularJS modules.

    • Answer: Modules are containers for related components (controllers, services, directives, etc.). They are used to organize and structure your application.

26. How do you create a custom module in AngularJS?

    • Answer: You create a custom module using the `angular.module` function. If the module doesn't exist it creates a new one otherwise it gets the existing module.

27. What is the digest cycle in AngularJS?

    • Answer: The digest cycle is the process by which AngularJS checks for changes in the scope and updates the View accordingly. It happens automatically, but you can trigger it manually using `$scope.$apply()`.

28. Explain the concept of dirty checking in AngularJS.

    • Answer: Dirty checking is the mechanism used in the digest cycle to detect changes in scope variables. AngularJS compares the current value of a variable with its previous value to see if it has been modified.

29. How does AngularJS handle events outside of the AngularJS context?

    • Answer: You can use `$scope.$apply()` to incorporate changes from outside AngularJS (like events from third-party libraries) into the AngularJS digest cycle.

30. What are some common AngularJS testing techniques?

    • Answer: Common techniques include unit testing (using frameworks like Jasmine and Karma) and end-to-end testing (using frameworks like Protractor).

31. Explain the benefits of using AngularJS for web application development.

    • Answer: Benefits include faster development, improved code maintainability, enhanced testability, and easier data management through two-way data binding.

32. What are some limitations of AngularJS?

    • Answer: Limitations include potential performance issues with large applications, a steeper learning curve compared to some other frameworks, and the fact that AngularJS is now largely superseded by Angular (version 2 and later).

33. What is the difference between AngularJS and Angular?

    • Answer: AngularJS (Angular 1.x) is a JavaScript framework, while Angular (version 2 and later) is a TypeScript-based framework with significant architectural differences, including a component-based architecture and improved performance.

34. How can you improve the performance of an AngularJS application?

    • Answer: Techniques include minimizing the number of watchers, using one-time binding (`::`), optimizing the digest cycle, and using appropriate data structures.

35. What are some best practices for writing AngularJS code?

    • Answer: Best practices include using a modular design, writing clean and well-commented code, following naming conventions, and using a consistent coding style.

36. How do you handle errors in AngularJS?

    • Answer: Error handling can be implemented using try-catch blocks, promises, and error callbacks within services and controllers, and utilizing AngularJS's built-in error handling mechanisms.

37. Explain how to implement form validation in AngularJS.

    • Answer: Form validation can be accomplished using built-in directives like `ng-required`, `ng-minlength`, `ng-maxlength`, and custom validation functions, along with providing user feedback through error messages.

38. How do you work with AJAX requests in AngularJS?

    • Answer: The `$http` service facilitates AJAX calls, allowing you to make GET, POST, PUT, DELETE requests to servers and handle responses, often using promises to manage asynchronous operations.

39. How to secure an AngularJS application?

    • Answer: Security measures include using HTTPS for all communication, proper input validation, output encoding, authentication and authorization mechanisms (often integrated with a backend system), and protection against cross-site scripting (XSS) attacks.

40. What are some common security vulnerabilities in AngularJS applications, and how can they be mitigated?

    • Answer: Common vulnerabilities include XSS, CSRF (Cross-Site Request Forgery), and SQL injection. Mitigation strategies involve input sanitization, output encoding, using parameterized queries (to prevent SQL injection), and implementing CSRF tokens.

41. Explain how you would integrate AngularJS with a RESTful API.

    • Answer: Integration involves using the `$http` service to make requests to the REST API endpoints (GET, POST, PUT, DELETE). The responses are then processed and used to update the application's data model.

42. How would you handle authentication and authorization in an AngularJS application?

    • Answer: Authentication and authorization typically involve interacting with a backend authentication service. Tokens (like JWTs) are often used to manage user sessions. Routes can be protected based on user roles and permissions.

43. Describe how you would implement a reusable component in AngularJS.

    • Answer: Reusable components are typically created as custom directives. These encapsulate the component's template, logic (controller), and styling into a self-contained unit that can be reused throughout the application.

44. Explain the concept of a directive's `link` function and `compile` function.

    • Answer: The `compile` function is executed only once during the directive's compilation phase. It manipulates the DOM before the directive's link function is called. The `link` function is executed during the linking phase and handles the actual data binding and DOM manipulation.

45. How to use isolated scopes in directives?

    • Answer: Isolated scopes prevent the directive from inheriting the parent scope's variables, thereby preventing unintended side effects. They are defined using the `scope` property in the directive definition object, typically with `@`, `=`, or `&` to bind properties.

46. What are the different types of isolated scope bindings in directives?

    • Answer: `@` (one-way binding from parent to child), `=` (two-way binding), and `&` (expression binding, allowing passing functions from the parent scope).

47. Explain how to create a directive that transcludes content.

    • Answer: Transclusion allows a directive to include the content of its element. This is achieved by setting the `transclude` property to `true` in the directive definition object and using `$transclude` in the directive's link function.

48. How do you optimize AngularJS performance for large datasets?

    • Answer: Techniques include pagination, using virtual scrolling, limiting the number of watchers, and filtering/sorting data on the server-side before sending it to the client.

49. How to handle asynchronous operations in AngularJS?

    • Answer: Asynchronous operations are handled using promises (returned by `$http` and other asynchronous services), callbacks, and the `$q` service for managing and chaining promises.

50. Explain how you would implement a custom animation in AngularJS.

    • Answer: Custom animations are created using the `$animate` service. This service allows you to define animations for various AngularJS events, such as adding, removing, or moving DOM elements. You typically define the animation using CSS classes or JavaScript functions.

51. How do you internationalize an AngularJS application?

    • Answer: Internationalization (i18n) involves using filters to format numbers, dates, and currencies according to the user's locale. It also involves using translation mechanisms (often involving JSON files containing translations) to display text in different languages.

52. How would you debug an AngularJS application?

    • Answer: Debugging techniques include using the browser's developer tools (console logging, breakpoints), utilizing AngularJS's debugging tools, and employing unit and integration testing to identify issues early in the development process.

53. What are some common AngularJS design patterns?

    • Answer: Common patterns include MVC, factory/service patterns for creating reusable components, and the observer pattern (implicitly used with two-way data binding).

54. Explain the use of $location service in AngularJS.

    • Answer: The `$location` service provides information about the current URL and allows modification of the URL without a full page reload, facilitating client-side routing.

55. How to use $timeout service in AngularJS?

    • Answer: The `$timeout` service executes a function after a specified delay (similar to `setTimeout`), ensuring proper integration with AngularJS's digest cycle.

56. What is the purpose of the $interval service in AngularJS?

    • Answer: The `$interval` service repeatedly executes a function at a specified interval, similar to `setInterval`, but with better integration with the AngularJS digest cycle, ensuring cleanups when the interval is cancelled.

57. How do you handle HTTP interceptors in AngularJS?

    • Answer: HTTP interceptors are used to intercept HTTP requests and responses before they reach the application's services. They are useful for tasks like adding headers (authentication tokens), transforming data, or logging requests. They are configured using `$httpProvider`.

58. How can you improve the SEO of an AngularJS application?

    • Answer: SEO optimization techniques include using server-side rendering (SSR) to make the application crawlable by search engines and implementing techniques to help search engines index the content correctly (such as meta tags).

59. What are some alternative JavaScript frameworks to AngularJS?

    • Answer: Popular alternatives include React, Vue.js, and Ember.js.

60. What is the ng-cloak directive in AngularJS?

    • Answer: The `ng-cloak` directive hides the content until AngularJS compiles it, preventing the display of uncompiled templates.

61. What are AngularJS expressions? How are they different from JavaScript expressions?

    • Answer: AngularJS expressions are similar to JavaScript expressions but with limitations. They are primarily used for data binding in templates and are evaluated within the AngularJS context. They do not support control flow statements (if/else, for loops), and only allow simple assignments, but not functions that modify data directly.

62. How do you create a reusable component using a directive? Provide a basic example.

    • Answer: You create a reusable component by defining a directive with a template and optionally a controller and link function. The template defines the component's HTML, and the controller handles the logic. The link function manages DOM interactions. A basic example would involve a directive that displays a user's name: `app.directive('userName', function() { return { restrict: 'E', scope: { user: '=' }, template: '

      User Name: {{user.name}}

      ' }; });`

63. Describe the lifecycle of a directive.

    • Answer: The lifecycle includes the compile phase (where the `compile` function is called, if defined), followed by the pre-link and post-link phases of the linking phase where the `link` function is called. The `compile` phase is for DOM manipulation before linking, while `link` handles data binding, DOM manipulation, and event handling during the linking phase.

64. What is the purpose of the `$parse` service in AngularJS?

    • Answer: The `$parse` service converts AngularJS expressions into functions that can be safely executed in the context of a scope.

65. How can you prevent AngularJS from executing an expression if a certain condition is not met?

    • Answer: Use `ng-if` to conditionally include/exclude part of the DOM, or use a ternary operator within an AngularJS expression to conditionally display data.

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