Angular Interview Questions and Answers

This section covers frequently asked Angular interview questions.

1. What is Angular?

Angular is a TypeScript-based open-source web application framework developed and maintained by Google. It's a powerful tool for building complex and scalable single-page applications (SPAs).

2. Powerful Features of Angular.

• Declarative templates
• End-to-end tooling
• Dependency injection
• Component-based architecture

3. Main Purpose of Angular.

Angular is used to create dynamic, efficient, and maintainable web applications. Its component-based structure makes it scalable and suitable for large projects.

4. AngularJS vs. Angular.

5. Advantages of Using Angular.

• Two-way data binding
• MVC architecture
• Component-based structure
• Custom directives
• RESTful service support
• Built-in validation
• Dependency injection
• Supports animations and event handling

6. Angular Expressions vs. JavaScript Expressions.

Angular expressions are used within templates to bind data to the UI. Key differences:

• Angular expressions are evaluated against the scope of the component; JavaScript expressions are evaluated against the global window object.
• Angular expressions handle null and undefined gracefully.
• Angular expressions don't allow control flow statements (loops, conditionals), but they utilize pipes for data transformation.

7. Templates in Angular.

Templates are HTML files containing Angular directives and expressions. They define the UI structure and how data from the component's model is displayed.

8. Annotations vs. Decorators.

In Angular, annotations provide metadata about a class; decorators are design patterns for modifying or extending classes without directly altering their source code.

9. Why Angular Was Introduced as a Client-Side Framework.

Early web development often involved complex and hard-to-maintain JavaScript code. Angular provided a structured, component-based approach that made building large-scale, dynamic web applications significantly easier.

10. How an Angular Application Works.

The `angular.json` file configures the application build process. The main.ts file is the application's entry point, bootstrapping the application module (e.g., AppModule) which contains the declarations of all the application's components.

13. What is the Scope Hierarchy in Angular?

AngularJS uses a hierarchical scope system, where scopes are used to manage data within a view. The root scope is at the top level; child scopes inherit from their parent scopes. This makes it simpler to manage data within the framework and allows each controller to have its own scope to manage data.

14. Main Building Blocks of an Angular Application.

(This section would include a diagram and description of the key components of an Angular application architecture, such as Modules, Components, Services, and Templates.)

15. Observables vs. Promises in Angular.

16. Ahead-of-Time (AOT) Compilation.

AOT compilation in Angular transforms your Angular code (templates and TypeScript) into efficient JavaScript code *before* the browser loads the application. This results in faster rendering and reduced bundle size.

17. Benefits of AOT Compilation.

• Faster rendering
• Smaller bundle size
• Fewer HTTP requests
• Earlier error detection
• Enhanced security

18. Just-in-Time (JIT) Compilation.

JIT compilation in Angular compiles the application code at runtime in the browser. This is typically used for development purposes.

19. JIT vs. AOT.

20. What is an Anonymous Object in Scala (Repeated from earlier section)?

An anonymous object in Scala is an object instance without a name. It's useful for creating objects that are used only once and don't require a named reference.

21. What is a Constructor in Scala (Repeated from earlier section)?

In Scala, constructors are part of the class definition itself. A primary constructor initializes the class's fields; auxiliary constructors use `this()` to invoke the primary constructor.

22. Method Overloading in Scala (Repeated from earlier section).

Method overloading is the ability to define multiple methods with the same name but with different parameter lists (either differing numbers of parameters or different parameter types).

23. The `this` Keyword in Scala (Repeated from earlier section).

The `this` keyword in Scala is used to refer to the current instance of an object (the object upon which the method is being called).

24. Inheritance in Scala (Repeated from earlier section).

Inheritance in Scala is achieved by using the `extends` keyword to create a subclass (or derived class) from a superclass (or base class).

25. Method Overriding in Scala (Repeated from earlier section).

Method overriding involves providing a specific implementation for a method already defined in a superclass within a subclass. The `override` keyword is mandatory in Scala.

26. The `final` Keyword in Scala (Repeated from earlier section).

The `final` keyword in Scala prevents a variable, method, or class from being overridden or extended.

27. Final Classes in Scala (Repeated from earlier section).

A final class cannot be extended.

28. Abstract Classes in Scala (Repeated from earlier section).

Abstract classes cannot be instantiated; they serve as blueprints for subclasses. They can have both abstract (unimplemented) and concrete (implemented) methods.

29. Scala Traits (Repeated from earlier section).

Traits are similar to interfaces in Java but can contain both abstract and concrete methods. A class can implement multiple traits.

30. Trait Mixins (Repeated from earlier section).

Trait mixins allow combining multiple traits into a single class.

31. Access Modifiers in Scala (Repeated from earlier section).

Access modifiers (private, protected, package-private, public) control the visibility of class members.

32. Arrays in Scala (Repeated from earlier section).

Arrays are mutable, indexed sequences of elements of the same type.

33. The `ofDim` Method in Scala (Repeated from earlier section).

The `ofDim` method creates multidimensional arrays.

34. Strings in Scala (Repeated from earlier section).

Strings are immutable sequences of characters.

35. String Interpolation in Scala (Repeated from earlier section).

String interpolation allows embedding expressions directly within string literals.

20. Observables: Synchronous and Asynchronous Behavior.

Promises are always asynchronous. Observables can be synchronous or asynchronous, depending on how they are created. The example from the original text shows that when an observable is created using `setTimeout`, the observable will execute after three seconds. This demonstrates the asynchronous nature of observables when used with a timer.

21. Directives in Angular.

Directives are classes decorated with @Directive. They modify the behavior of existing DOM elements or create new ones. They can be applied to modify HTML elements or create new elements entirely.

22. Reasons for Introducing Client-Side Frameworks.

Client-side frameworks like Angular addressed challenges in managing complex JavaScript code and data handling across views in traditional web development. They offered improved structure, modularity, and maintainability compared to using only Vanilla JavaScript or jQuery.

23. Angular CLI (Command Line Interface).

Angular CLI is a command-line tool for creating, building, and managing Angular projects. It simplifies common development tasks.

ng new my-project       // Creates a new project
ng generate component my-component // Generates a component
ng serve                // Starts a development server

24. Lazy Loading in Angular.

Lazy loading improves application load times by loading modules only when needed. It uses the loadChildren property in route definitions.

const routes: Routes = [
  {
    path: 'employees',
    loadChildren: () => import('./employees/employees.module').then(m => m.EmployeesModule)
  }
];

25. Angular Router.

The Angular Router manages navigation between different views in a single-page application.

26. Router Imports.

The Angular Router is a separate module that must be imported into your application (usually in your app module).

27. RouterOutlet and RouterLink.

RouterOutlet is a directive that serves as a placeholder for components. RouterLink is a directive that makes anchor tags navigable within the application using the Angular router.

28. Router Events.

(List the various router events that the Angular router emits.)

29. RouterLinkActive.

RouterLinkActive adds CSS classes to active links in navigation menus.

30. RouterState.

The `RouterState` provides information about the currently active route in an Angular application.

31. HttpClient.

HttpClient is Angular's simplified API for making HTTP requests to backend services. It returns Observables.

32. Server-Side Rendering with Angular Universal.

Angular Universal allows rendering Angular applications on the server. This improves initial load times and SEO.

33. Error Handling in Angular.

(This section describes how to handle errors returned by `HttpClient`, often using error callbacks in `subscribe()`.)

34. Angular Bootstrapping.

Bootstrapping initializes the Angular application. It can be manual or automatic (using the `ng-app` directive).

35. Angular Digest Cycle.

The digest cycle is Angular's process for detecting and applying changes to the model.

36. Component vs. Directive.

20. Observables: Synchronous and Asynchronous Behavior (Continued).

Observables, unlike Promises, can be both synchronous and asynchronous. The example demonstrates an asynchronous observable using `setTimeout`, showcasing that the observable doesn't emit a value until the timer expires.

21. Directives in Angular.

Directives modify the behavior of DOM elements or create new ones. They're used to add functionality to HTML, often making components more reusable and efficient. They are declared using the `@Directive` decorator.

22. Reasons for Client-Side Frameworks.

Client-side frameworks like Angular offer solutions to challenges in managing complex JavaScript code, maintaining separation of concerns, and handling data across views in traditional web development. They provide structure and modularity.

23. Angular CLI.

Angular CLI (Command Line Interface) is a command-line tool for scaffolding and managing Angular projects. It streamlines development processes.

24. Lazy Loading in Angular.

Lazy loading loads modules on demand, improving initial load times, especially beneficial for large applications with many routes.

25. Angular Router.

The Angular router manages client-side navigation between different views or components within a single-page application.

26. Router Imports.

Importing necessary modules from the @angular/router package into your application modules (typically the app module) to enable routing functionality.

27. RouterOutlet and RouterLink.

RouterOutlet is a directive that specifies where the router should display the currently active component. RouterLink is a directive that allows you to create links for navigation within your application using the Angular router.

28. Router Events.

(This section would list and explain the events that the Angular router emits, such as `NavigationStart`, `NavigationEnd`, `NavigationCancel`, `NavigationError`, etc.)

29. RouterLinkActive.

RouterLinkActive dynamically applies CSS classes to active navigation links.

30. RouterState.

RouterState provides information about the current route, including parameters and data.

31. HttpClient.

HttpClient provides a simplified API for making HTTP requests in Angular, offering features like type safety, interceptors, and observable-based responses.

32. Server-Side Rendering in Angular.

Angular Universal enables server-side rendering of Angular applications, improving initial load times and SEO.

33. Error Handling with HttpClient.

(This section would detail how to handle HTTP errors using error callbacks within the `subscribe()` method.)

34. Angular Bootstrapping.

Bootstrapping initializes the Angular application. It can be done manually or automatically (using the `ng-app` directive in AngularJS, though this approach is outdated in modern Angular versions).

35. Angular Digest Cycle.

The digest cycle is the process where Angular detects changes to the application model and updates the view accordingly.

36. Component vs. Directive.

37. Angular MVVM (Model-View-ViewModel) Architecture.

MVVM is a design pattern separating the UI (View), data (Model), and presentation logic (ViewModel). The ViewModel acts as an intermediary between the Model and View.

38. AsyncPipe.

AsyncPipe subscribes to Observables or Promises and automatically updates the view with the latest emitted value.

39. Services in Angular.

Services are singleton objects that provide functionalities (data access, business logic) reusable across components.

40. Constructor vs. ngOnInit.

The constructor is for basic initialization; ngOnInit is for Angular-specific initialization (setting up data bindings, subscriptions, etc.).

41. Observable and Observer.

An observable is a stream of data. An observer is a handler listening for and reacting to changes emitted by an observable.

42. Data Binding Types.

Angular supports various data binding types, including one-way (from source to view or vice-versa) and two-way data binding.

43. Multicasting.

Multicasting allows an Observable to broadcast values to multiple observers simultaneously.

44. Angular Material.

Angular Material is a UI component library based on Material Design principles providing pre-built components.

45. Lazy Loading (Repeated from earlier).

Improves initial load times by loading modules only when needed.

46. Angular Filters.

(This section would describe Angular's built-in filters and how to create custom filters.)

47. When to Use Directives.

Directives are used to add behavior to existing elements or create reusable UI components.

48. Types of Directives.

• Component Directives
• Structural Directives (*ngIf, *ngFor)
• Attribute Directives

37. Components vs. Directives in Angular (Continued).

Components are directives with templates; they create encapsulated UI elements. Directives modify existing DOM elements.

38. Angular MVVM Architecture.

MVVM (Model-View-ViewModel) separates the UI (View), data (Model), and presentation logic (ViewModel). Two-way data binding connects the View and ViewModel.

39. AsyncPipe.

The AsyncPipe subscribes to Observables or Promises and automatically updates the view when a new value is emitted. It handles subscriptions and unsubscribes automatically, preventing memory leaks.

40. Services in Angular.

Services are singleton objects providing reusable functionality (data access, business logic) across components.

41. Constructor vs. ngOnInit.

Use the constructor for basic object initialization. Use ngOnInit for Angular-specific initialization after the component has been created.

42. Observable and Observer.

An Observable is a stream of asynchronous data. An Observer is a function that subscribes to the Observable and reacts to data emissions.

43. Data Binding Types in Angular.

Angular supports various data binding types (one-way and two-way), each with different syntax and data flow directions.

44. Multicasting in Angular.

Multicasting allows an Observable to send its emissions to multiple observers simultaneously.

45. Angular Material.

Angular Material provides pre-built UI components based on Google's Material Design specifications.

46. Lazy Loading (Repeated from earlier section).

Improves load times by delaying the loading of modules until they're needed.

47. Angular Filters.

(This section would detail how Angular filters format data for display in templates.)

48. When to Use Directives.

Use directives to add behavior to elements or create reusable UI components.

49. Types of Directives (Repeated from earlier section).

Component, Structural, and Attribute Directives.