20 Angular Testing Interview Questions and Answers

Angular is a popular web development framework used by many developers to create dynamic and interactive web applications. If you’re applying for a position that involves Angular development, it’s likely that you’ll be asked questions about how you would carry out testing. Answering these questions correctly can help you demonstrate your understanding of the Angular framework and your ability to carry out testing effectively. In this article, we discuss some of the most common Angular testing questions and how you should answer them.

Angular Testing Interview Questions and Answers

Here are 20 commonly asked Angular Testing interview questions and answers to prepare you for your interview:

1. What is Angular?

Angular is a JavaScript framework for building web applications and SPAs. It is used for creating reusable components, which can be used in different parts of an application. Angular is also used for unit testing and end-to-end testing of web applications.

2. When did Angular 1.0 get released and what was it called at the time of its initial release?

Angular 1.0 was released in October 2010 and was originally called AngularJS.

3. How do you create a new component in Angular?

In Angular, you can use the CLI to generate a new component. To do so, you would use the command “ng generate component component-name”. This will create a new component with the given name and add it to your project.

4. Can you explain how to add an event binding in Angular?

You can add an event binding in Angular by using the ( ) notation around the event you want to bind to. For example, if you wanted to bind to the click event of a button, you would use (click)=”someFunction()” in your template.

5. What are some common directives used in Angular?

Some common directives used in Angular are ng-app, ng-controller, ng-repeat, and ng-show.

6. Why is dependency injection important in Angular?

Dependency injection is important in Angular because it allows for greater flexibility and modularity in the code. By injecting dependencies, we can more easily change the behavior of our code without having to make major changes to the code itself. This can be especially useful in unit testing, where we can mock dependencies to more easily test our code.

7. What’s the difference between constructor and ngOnInit?

The constructor is a default method of the class that is executed when the class is instantiated. The ngOnInit is a lifecycle hook that is called after the constructor and after the first ngOnChanges.

8. How can communication be achieved between components in Angular?

Communication in Angular can be achieved between components using a number of methods. One way is to use the @Input and @Output decorators. The @Input decorator allows data to be passed down from a parent component to a child component. The @Output decorator allows data to be passed up from a child component to a parent component. Another way to achieve communication is to use a shared service. A shared service is a service that can be injected into any number of components and provides a way for those components to share data and communicate with each other.

9. What’s the use of @angular/http module?

The @angular/http module provides a way to make HTTP requests from Angular applications. It also provides a number of helper functions for dealing with common HTTP tasks, such as parsing headers and JSON data.

10. Name some ways in which data can be shared between components in Angular?

There are a few ways in which data can be shared between components in Angular:

1. Services: Services can be used to share data between components. Services are singletons, meaning that there is only one instance of the service in the application. This means that any data that is stored in the service can be accessed by any component that injects the service.

2. Input/Output: Components can share data using the @Input and @Output decorators. @Input allows data to be passed into a component from its parent, while @Output allows data to be emitted from a component to its parent.

3. BehaviorSubjects: BehaviorSubjects are a type of observable that allows components to subscribe to a stream of data that can be emitted from another component. This is useful for sharing data that may be updated over time, such as a user’s current location.

11. What is AOT compilation?

AOT compilation is a ahead-of-time compilation process that compiles Angular components and modules before they are run. This process makes Angular apps faster and more secure, as it eliminates the need for the browser to compile Angular code on the fly.

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

AOT is a process of compiling Angular components and their templates at build time, before the browser downloads and runs that code. This can result in significant performance gains, as the browser doesn’t have to waste time compiling the code on the fly. It also allows for more secure code, as the compiled code is more difficult to tamper with.

13. What is Lazy Loading in Angular?

Lazy loading is a technique used in Angular to load modules only when they are needed. This can improve the performance of an Angular application by loading modules only when they are needed, instead of loading all modules upfront.

14. What are the different types of guards in Angular?

There are four different types of guards in Angular: CanActivate, CanDeactivate, CanLoad, and Resolve. CanActivate is used to determine if a route can be activated, while CanDeactivate is used to determine if a route can be deactivated. CanLoad is used to prevent lazy-loaded modules from being loaded until the guard conditions are met, and Resolve is used to pre-fetch data before a route is activated.

15. Is there any way to combine two or more routes into one route? If yes, then how?

Yes, there is a way to combine two or more routes into one route. This can be done by using the “redirectTo” property of the route configuration object. The “redirectTo” property takes a string that specifies the path to which the route should redirect.

16. What is the purpose of using Pure Pipes in Angular?

Pure pipes are used in Angular to only re-evaluate a pipe when the input to the pipe changes. This means that if the input to the pipe is an object, the pipe will only re-evaluate when the object reference changes. This can be useful for performance reasons, as re-evaluating a pipe can be expensive.

17. What does the * character mean when used with an attribute?

The * character is used as a wildcard when used with an attribute. This means that the attribute will match any value that is given, regardless of what it is.

18. Can you give me an example of how you would code a custom service in Angular?

In Angular, a service is simply a class that can be used to provide some sort of functionality to your application. For example, you could create a service that handles all of the data storage and retrieval for your application. To code a custom service, you would simply create a new class and then register it with the Angular injector.

19. What is the difference between Observable and Promises?

Observables are lazy, meaning that they do not start emitting values until they are subscribed to. Promises, on the other hand, are eager, meaning they will start emitting values as soon as they are created.

20. What is the best way to test your Angular application?

There is no one-size-fits-all answer to this question, as the best way to test your Angular application will vary depending on the specific application and what you are trying to test. However, some general tips that may be helpful include using a unit testing framework such as Jasmine or Mocha to write and run your tests, and using a headless browser such as PhantomJS to run your tests in a real browser environment.