1. What is Angular?

Angular is an open-source JavaScript framework used for building single-page web applications. It is maintained by Google and has a rich set of features for creating complex web applications.

2. What is TypeScript?

TypeScript is a superset of JavaScript that adds features such as static typing, classes, and interfaces to the language. It is designed to make it easier to build large-scale applications and to catch errors at compile-time instead of runtime.

3. What is the difference between AngularJS and Angular?

AngularJS is the first version of Angular, while Angular is a complete rewrite with improved performance, features, and architecture. Angular also uses TypeScript, while AngularJS uses JavaScript.

4. What is a component in Angular?

A component in Angular is a building block for creating a user interface. It consists of an HTML template, a class that defines the logic of the component, and styles that define the appearance of the component.

5. What is a directive in Angular?

A directive in Angular is a way to add behavior to existing HTML elements or create custom elements. Directives can be used to create reusable components and to manipulate the DOM.

6. What is a service in Angular?

A service in Angular is a class that provides functionality to multiple components. Services are typically used to encapsulate business logic, data access, or other common functionality.

7. What is a module in Angular?

A module in Angular is a container for related components, directives, pipes, and services. It provides a way to organize an application into functional units and to manage the dependencies between them.

8. What is dependency injection in Angular?

Dependency injection in Angular is a design pattern used to provide dependencies to a class without creating them inside the class. This makes it easier to write testable code and to decouple the components of an application.

9. What is lazy loading in Angular?

Lazy loading in Angular is a technique that loads a module only when it is required. This can improve the performance of an application by reducing the initial load time and only loading the necessary components when they are needed.

10. What is a route in Angular?

A route in Angular is a mapping between a URL and a component or a module. It provides a way to navigate between different views or pages of an application.

11. What is a router outlet in Angular?

A router outlet in Angular is a placeholder where the content of a component or a module is rendered based on the current route. It is used to dynamically load components or modules based on the user's navigation.

12. What is data binding in Angular?

Data binding in Angular is a way to synchronize the data between the component class and the HTML template. There are several types of data binding in Angular, including one-way, two-way, and event binding.

13. What is a template in Angular?

A template in Angular is an HTML file that defines the structure of a component or a module. It can contain placeholders for dynamic data, and it can be used to create reusable components.

14. What is a two-way data binding in Angular?

Two-way data binding in Angular is a way to synchronize the data between the component class and the HTML template in both directions. It uses the [(ngModel)] syntax in the template to update the data in the component class and vice versa.

15. What is a form in Angular?

A form in Angular is a way to capture and validate user input. Angular provides two types of forms: template-driven forms and reactive forms.

16. What is a reactive form in Angular?

A reactive form in Angular is a form that is built using reactive programming techniques. It provides a more flexible and scalable way to handle complex forms with dynamic behavior and validation.

17. What is the difference between template-driven forms and reactive forms in Angular?

Template-driven forms in Angular are built using directives in the template and are based on two-way data binding. Reactive forms, on the other hand, are built programmatically using Reactive Forms API and are based on reactive programming techniques. Reactive forms provide more control, flexibility, and scalability, especially for complex forms.

18. What is an observable in Angular?

An observable in Angular is a data stream that can emit multiple values over time. It is used extensively in Angular for handling asynchronous operations, such as HTTP requests, and for implementing reactive programming patterns.

19. What is a pipe in Angular?

A pipe in Angular is a way to transform data before displaying it in the template. Pipes can be used to format dates, currency, text, and other types of data. Angular provides several built-in pipes and allows you to create custom pipes.

20. What is the difference between pure and impure pipes in Angular?

Pure pipes in Angular are stateless and produce the same output for the same input. They are optimized for performance and are only called when the input value changes. Impure pipes, on the other hand, can have side effects and are called on every change detection cycle. They should be used sparingly and with caution.

21. What is a resolver in Angular?

A resolver in Angular is a service that pre-fetches data before a route is activated. It ensures that the necessary data is available before the component is rendered, which can improve the performance and user experience of an application.

22. What is NgZone in Angular?

NgZone in Angular is a service that provides a way to run code inside or outside the Angular zone. The Angular zone is a virtual boundary that defines the context in which Angular operates. Running code outside the zone can improve the performance of an application by reducing the frequency of change detection cycles.

23. What is change detection in Angular?

Change detection in Angular is a process that detects and updates the changes in the component's data and the DOM. It is triggered automatically by Angular and can also be triggered manually using the ChangeDetectorRef service.

24. What is a resolver in Angular?

A resolver in Angular is a service that pre-fetches data before a route is activated. It ensures that the necessary data is available before the component is rendered, which can improve the performance and user experience of an application.

25. What is a content projection in Angular?

Content projection in Angular is a way to pass content from a parent component to a child component. It is used to create reusable components and to create dynamic content based on the context of the application.

26. What is a view encapsulation in Angular?

View encapsulation in Angular is a way to isolate the styles of a component from the rest of the application. It provides three modes: Emulated, Native, and None, and allows you to control the scope and visibility of the styles.

27. What is zone.js in Angular?

Zone.js in Angular is a library that provides a way to patch the native JavaScript APIs to add hooks for change detection and error handling. It is used by Angular to implement the change detection mechanism and to run code inside or outside the Angular zone.

28. What is Angular Universal?

Angular Universal is a server-side rendering solution for Angular applications. It allows the application to be rendered on the server and sent to the client as HTML, which can improve the performance, SEO, and accessibility of the application.

29. What is AOT compilation in Angular?

AOT (Ahead-of-Time) compilation in Angular is a process that compiles the application code during the build time, rather than at runtime. It can improve the performance of an application by reducing the size and complexity of the application code.

30. What is the difference between NgModule and Component in Angular?

NgModule in Angular is a decorator that defines a module, which is a container for a group of related components, directives, services, and pipes. A component, on the other hand, is a decorator that defines a reusable UI component, which can be composed of other components, directives, and services.

31. What is a directive in Angular?

A directive in Angular is a way to add behavior to an existing DOM element or to create a new custom element. There are two types of directives in Angular: structural directives and attribute directives.

32. What is a service in Angular?

A service in Angular is a singleton object that provides functionality across an application. It can be used for data sharing, communication with the backend, and for implementing business logic.

33. What is Dependency Injection (DI) in Angular?

Dependency Injection (DI) in Angular is a design pattern that allows the components and services to be loosely coupled by providing dependencies through the constructor or property injection. It allows for better testing, maintainability, and scalability of an application.

34. What is a route guard in Angular?

A route guard in Angular is a way to control the access to a route based on certain conditions, such as authentication or user roles. There are three types of route guards in Angular: CanActivate, CanActivateChild, and CanDeactivate.

35. What is an interceptor in Angular?

An interceptor in Angular is a middleware that intercepts HTTP requests and responses and can modify or transform them before they are sent to the server or received by the client. It is used for adding headers, logging, error handling, and for implementing caching and authentication.

36. What is the purpose of the @ViewChild decorator in Angular?

The @ViewChild decorator in Angular is used to get a reference to a child component, directive, or DOM element in the parent component. It allows the parent component to interact with the child component or to access its properties or methods.

37. What is the purpose of the ng-content directive in Angular?

The ng-content directive in Angular is used to pass content from the parent component to the child component using content projection. It allows the child component to receive dynamic content and to display it based on the context of the application.

38. What is the purpose of the ng-template directive in Angular?

The ng-template directive in Angular is used to define a template that can be reused by other components or directives using content projection. It allows for better code organization, reusability, and maintainability of an application.

39. What is the purpose of the Renderer2 service in Angular?

The Renderer2 service in Angular is used to interact with the DOM in a safe and efficient way, without directly manipulating the DOM. It provides a platform-independent API for creating, updating, and deleting DOM elements and attributes, and for handling events.

40. What is the difference between ViewChildren and ContentChildren in Angular?

ViewChildren in Angular is used to get a reference to the child components or directives that are declared in the view of the parent component. ContentChildren, on the other hand, is used to get a reference to the child components or directives that are projected into the view of the parent component using ng-content.

41. What is the difference between ngOnInit and ngAfterViewInit in Angular?

ngOnInit in Angular is a lifecycle hook that is called after the component has been initialized and the inputs have been bound. ngAfterViewInit, on the other hand, is called after the view of the component has been initialized and the child components and directives have been rendered.

42. What is the purpose of the ngIf directive in Angular?

The ngIf directive in Angular is used to conditionally render a part of the template based on a boolean expression. It allows for dynamic content and can be used for showing or hiding elements, or for rendering different parts of the template based on the current state of the application.

43. What is a template reference variable in Angular?

A template reference variable in Angular is a variable that can be defined on an HTML element using the # symbol, which can be used to refer to that element or component in the component's code or template.

44. What is the difference between ngOnChanges and ngDoCheck in Angular?

ngOnChanges in Angular is a lifecycle hook that is called whenever one or more input properties of a component change. ngDoCheck, on the other hand, is called whenever the change detection mechanism of Angular detects changes in the component's template or bindings.

45. What is the difference between ngOnInit and constructor in Angular?

constructor in Angular is the first method that is called when a component is instantiated. ngOnInit, on the other hand, is a lifecycle hook that is called after the inputs of the component have been bound and the component has been initialized. It is used for initialization tasks that depend on the component's inputs.

46. What is the purpose of the async pipe in Angular?

The async pipe in Angular is used to subscribe to an Observable or Promise in the template and to automatically handle the subscription and unsubscription of the Observable or Promise. It allows for better code readability and simplifies the management of asynchronous data.

47. What is NgZone in Angular?

NgZone in Angular is a service that provides a zone where Angular can execute its change detection mechanism. It is used for running code outside of the Angular zone, which can improve the performance of the application.

48. What is the difference between Observables and Promises in Angular?

Observables in Angular are a way to handle asynchronous data streams, which can emit multiple values over time. Promises, on the other hand, are a way to handle asynchronous operations that can only emit a single value. Observables can be cancelled, retried, or composed, while Promises cannot.

49. What is the purpose of the Angular CLI?

The Angular CLI (Command Line Interface) is a tool that is used for creating, managing, and building Angular applications. It provides a set of commands for generating components, services, modules, and other Angular artifacts, and for managing dependencies, testing, and deployment.

50. What is Ahead-of-Time (AOT) compilation in Angular?

Ahead-of-Time (AOT) compilation in Angular is a process of compiling the application code during the build time, instead of compiling it in the browser at runtime using Just-in-Time (JIT) compilation. It can improve the performance and the size of the application and can eliminate the need for a JIT compiler in the browser.