Angular Interview Questions

1.      What is Angular?

Ans: Angular is a platform and framework for building web applications using TypeScript and JavaScript. It is an open-source project developed and maintained by Google.

2.      What are the key features of Angular?

Ans: Some of the key features of Angular include: component-based architecture, two-way data binding, dependency injection, a powerful template language, and support for dynamic loading.

3.      How does Angular differ from AngularJS?

Ans: Angular is a complete rewrite of AngularJS and is not backward-compatible. Angular uses a component-based architecture, whereas AngularJS uses a directive-based architecture. Additionally, Angular uses a more powerful template language and has improved performance.

4.      How does data binding work in Angular?

Ans: Angular uses a two-way data binding approach, which means that when a user interacts with an element on the page, the corresponding component's property is automatically updated, and when the component's property is updated, the element on the page is automatically updated.

5.      What is a component in Angular?

Ans: A component in Angular is a building block of the application that controls a portion of the screen. It is a class that contains a template, data, and logic. A component can also have child components, which are called nested components.

6.      What is dependency injection in Angular?

Ans: Dependency injection is a design pattern that allows Angular to provide dependencies to a component. It is a way for a component to access services or other objects that it needs to perform its tasks. Angular uses a powerful Dependency Injection (DI) system that makes it easy to manage dependencies throughout an application.

7.      What is the role of a module in Angular?

Ans: A module in Angular is a container for a group of related components, directives, pipes, and services. Modules help organize an application and make it easier to manage. The root module is the starting point of the application and other modules can be loaded as needed.

8.      What is a directive in Angular?

Ans: A directive in Angular is a class that adds behavior to an element in the template. Directives can be used to create custom elements or to change the behavior of existing elements. Angular provides several built-in directives, such as ngIf and ngFor, but you can also create custom directives.

9.      What is a service in Angular?

Ans: A service in Angular is a class that contains methods that can be used across multiple components in an application. Services are used to share data and logic between components and are typically used for tasks such as making HTTP requests, logging, and performing calculations.

10.   What is the role of the router in Angular?

Ans: The router in Angular is responsible for handling navigation between different components in an application. It uses a component-based approach to navigation and allows you to define routes, which map URLs to specific components. The router also supports features such as lazy loading, which allows you to load parts of an application only when they are needed.

11.   What is an observable in Angular?

Ans: An observable in Angular is a way to handle asynchronous data streams. It is similar to a promise but can handle multiple values over time. Observables are used in Angular for tasks such as handling HTTP requests and handling user input.

12.   What is the difference between a component and a directive in Angular?

Ans: A component in Angular is a building block of the application that controls a portion of the screen, whereas a directive in Angular is a class that adds behavior to an element in the template. Both components and directives are used to extend the functionality of HTML, but components are used to create custom elements and handle logic and data, while directives are used to change the behavior of existing elements.

13.   What is the difference between a pipe and a filter in Angular?

Ans: Both pipes and filters in Angular are used to transform data in a template, but pipes are the standard way to do this in Angular. Pipes are a feature of the template language and are used to format data for display. Filters, on the other hand, are a feature of AngularJS (the version before Angular) and are not used in Angular.

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

Ans: The constructor in Angular is a method that is called when a component is created, whereas the ngOnInit method is called after the constructor and is used to perform any additional initialization tasks. The constructor is used to initialize the class and its properties, while ngOnInit is used to set up any logic or data that is needed by the component.

15.   How does change detection work in Angular?

Ans: Change detection in Angular is the process of updating the view when the data in a component changes. Angular uses a mechanism called dirty checking, which compares the current value of a property with the previous value to determine if the view needs to be updated. Angular also supports OnPush change detection, which reduces the number of change detection checks by only checking components that have been marked as changed.

16.   Explain the difference between ngModel and [(ngModel)] in Angular?

Ans: ngModel is a directive in Angular that allows two-way data binding between a form element and a component property. [(ngModel)] is the syntax for property binding and event binding together, which means it binds the value of the component property to the value of the form element and also listens to the change event of the form element. So, when the form element value changes, the component property also updates and vice-versa.

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

Ans: A template-driven form in Angular is a way to create forms using directives and the template, while a reactive form is a way to create forms using a programmatic approach. In a template-driven form, the template defines the form structure and validation, while in a reactive form, the component defines the form structure and validation using a FormGroup and FormControl objects.

18.   Explain the use of ngFor directive in Angular?

Ans: The ngFor directive in Angular is used to loop over an array or an iterable object and create a template for each item. It is used to create dynamic lists and tables in the template. The ngFor directive creates a new template for each item and adds it to the DOM. It is a powerful directive and can be used for many purposes.

19.   Explain the use of ngIf directive in Angular?

Ans: The ngIf directive in Angular is used to conditionally add or remove an element from the DOM. It is used to conditionally render a template based on a boolean expression. The ngIf directive adds the element to the DOM if the expression is true and removes it if the expression is false. It is a powerful directive and can be used for many purposes.

20.   What is the use of ngSwitch in Angular?

Ans: The ngSwitch directive in Angular is used to conditionally render elements based on the value of an expression. It is similar to a switch statement in other programming languages, where it selects one of the multiple possible templates based on the value of the switch expression. It is useful when we have multiple possible templates based on different conditions.

21.   How does Angular handle browser history and navigation?

Ans: Angular uses the Angular Router to handle browser history and navigation. The Angular Router is a powerful module that allows you to define routes in your application, which map URLs to specific components. When a user clicks on a link or enters a URL in the browser, the router uses the defined routes to navigate to the corresponding component. It also allows for navigation using the browser's back and forward buttons.

22.   What is the use of a guard in Angular?

Ans: A guard in Angular is a class that implements the CanActivate, CanDeactivate or CanLoad interface. It is used to control access to routes in the application. A guard can be used to check if a user is logged in or has the necessary permissions before allowing access to a route. It can also be used to prevent a user from navigating away from a route before saving unsaved changes.

23.   What is the use of a resolver in Angular?

Ans: A resolver in Angular is a class that is used to pre-fetch data before the component is created. A resolver is used to fetch data before navigating to a route, so that the component has the data it needs to display. This improves the user experience by avoiding the delay caused by fetching data after the component is created.

24.   What is the use of the async pipe in Angular?

Ans: The async pipe in Angular is a convenient way to subscribe and unsubscribe to an observable in the template. It automatically subscribes to the observable when the component is created and unsubscribes when the component is destroyed. The async pipe also takes care of error handling and sets the component property to the latest value emitted by the observable.

25.   How can you improve the performance of an Angular application?

Ans: There are several ways to improve the performance of an Angular application:

·        Use the OnPush change detection strategy

·        Use lazy loading to load parts of the application only when they are needed

·        Use the AOT (Ahead-of-Time) compiler to pre-compile the application

·        Use the ngIf directive instead of ngShow and ngHide

·        Use the trackBy function in the ngFor directive to improve the performance of dynamic lists

·        Use the immutable data structures

·        Use the immutable.js library to handle immutable data structures

·        Use the browser's caching mechanism to cache static assets

26.   Explain the use of the Renderer2 in Angular

Ans: The Renderer2 in Angular is an abstraction of the underlying renderer. It allows you to interact with the DOM using a platform-agnostic API. The Renderer2 class provides a way to create and manipulate elements, add and remove classes, set styles, and more. It is useful when you need to update the DOM outside of the Angular zone, or when you need to write platform-specific code.

27.   What is the use of the ng-template in Angular?

Ans: The ng-template in Angular is a way to define an HTML template that can be reused multiple times in the application. It is used to create reusable templates that can be used in different parts of the application. It can be used with the ngIf and ngFor directives to conditionally render elements in the template. It is also useful for creating reusable components.

28.   Explain the use of the ngModelGroup in Angular?

Ans: The ngModelGroup directive in Angular is used to group a set of form controls together. It allows you to apply validation and styles to a group of form controls, rather than having to apply them to each control individually. It also allows you to nest form groups within other form groups.

29.   Explain the use of the ngContent in Angular?

Ans: The ngContent directive in Angular is used to project content from a parent component into a child component. It is used to create reusable components that can accept content from the parent component and display it. ngContent is used in the child component's template to define the location where the projected content should be inserted.

30.   Explain the use of the ngClass directive in Angular?

Ans: The ngClass directive in Angular is used to add or remove CSS classes from an element based on an expression. It allows you to dynamically set CSS classes on an element based on the component's state or the value of a property. It can be used with a string, an object, or an array to set one or multiple classes.

31.   Explain the use of the ngStyle directive in Angular?

Ans: The ngStyle directive in Angular is used to set inline styles on an element based on an expression. It allows you to dynamically set styles on an element based on the component's state or the value of a property. It can be used with a string, an object, or an array to set one or multiple styles.

32.   What is the use of the ngPluralize directive in Angular?

Ans: The ngPluralize directive in Angular is used to conditionally render elements based on the value of a number. It allows you to display different messages based on the value of a number. It can be used to display a message like "1 item" or "2 items" based on the value of a property.

33.   Explain the use of the ngSwitch directive in Angular?

Ans: The ngSwitch directive in Angular is used to conditionally render elements based on the value of an expression. It is similar to a switch statement in other programming languages, where it selects one of the multiple possible templates based on the value of the switch expression. It is useful when we have multiple possible templates based on different conditions.

34.   Explain the use of the ngFor directive in Angular?

Ans: The ngFor directive in Angular is used to loop over an array or an iterable object and create a template for each item. It is used to create dynamic lists and tables in the template. The ngFor directive creates a new template for each item and adds it to the DOM. It is a powerful directive and can be used for many purposes.

35.   What is the use of the ngIf directive in Angular?

Ans: The ngIf directive in Angular is used to conditionally add or remove an element from the DOM. It is used to conditionally render a template based on a boolean expression. The ngIf directive adds the element to the DOM if the expression is true and removes it if the expression is false. It is a powerful directive and can be used for many purposes.

36.   Explain the use of the ngModel directive in Angular?

Ans: The ngModel directive in Angular is used to create two-way data bindings between a form element and a component property. It allows you to synchronize the value of a form element with a component property and vice versa. The ngModel directive supports validation, events, and more. It is used extensively in template-driven forms.

37.   Explain the use of the ngStyle directive in Angular?

Ans: The ngStyle directive in Angular is used to set inline styles on an element based on an expression. It allows you to dynamically set styles on an element based on the component's state or the value of a property. It can be used with a string, an object, or an array to set one or multiple styles.

38.   Explain the use of the ngClass directive in Angular?

Ans: The ngClass directive in Angular is used to add or remove CSS classes from an element based on an expression. It allows you to dynamically set CSS classes on an element based on the component's state or the value of a property.