20 Observables Interview Questions and Answers

Observables are a type of programming that allows developers to work with asynchronous data streams. This can be useful when working with data that is constantly changing, such as user input or stock prices. If you’re interviewing for a position that involves working with observables, it’s important to be prepared to answer questions about your experience and knowledge. In this article, we discuss some common observables interview questions and how you can answer them.

Observables Interview Questions and Answers

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

1. What is an Observable?

An Observable is an object that can be used to emit a stream of data. This data can be anything, from a simple value (like a number) to more complex objects (like an array). Observables are used in a variety of places, such as in AngularJS to handle asynchronous events.

2. Can you explain what an asynchronous observable is?

An asynchronous observable is an observable that emits values asynchronously. This means that the values emitted by the observable are not determined by when the observable is subscribed to, but by some other event. For example, an asynchronous observable may emit values when a certain timer goes off, or when a certain API call returns.

3. How do you define an Observable in JavaScript?

An Observable is a function that creates an Observer and attaches it to the Observable. The Observable then notifies the Observer of any changes, either to the data being observed or to the status of the Observable itself.

4. What are the different types of operators available for observables?

There are a variety of operators available for observables, depending on what you are trying to achieve. Some of the more common operators include map (to transform the data emitted by an observable), filter (to only emit certain values from an observable), and merge (to combine multiple observables into one).

5. What are “cold” and “hot” observables?

“Cold” observables are those that begin emitting items only when they are subscribed to. “Hot” observables, on the other hand, begin emitting items as soon as they are created, regardless of whether or not they have any subscribers.

6. What’s the difference between a Promise and an Observable?

A promise is an object that represents the result of an asynchronous operation. A promise can be in one of three states: pending, fulfilled, or rejected. Once a promise is fulfilled or rejected, it is immutable (i.e. it can’t be changed).

An observable is a stream of values that can be emitted over time. An observable can be created from a promise, but it can also be created from other data sources, such as an array. Unlike a promise, an observable can be canceled, and it can also be retried if it fails.

7. What options are available to create an Observable object?

There are many ways to create an Observable object. You can use the Observable constructor, use a function that returns an Observable, or use an array or promise that will be converted into an Observable.

8. What is an operator?

In RxJS, an operator is a function that takes a source observable as its input and outputs a new observable. There are many different types of operators, each with a different purpose. Some operators perform transformation on the data emitted by the source observable, while others filter the data or combine multiple observables.

9. What type of data can be used with an Observable in Angular 2?

An Observable can use any type of data. However, in Angular 2, an Observable is often used with an RxJS library to work with data streams.

10. Can you give me some examples of how observables are used in real world applications?

Observables are used in a variety of different ways in real world applications. One common use is in data binding, where an observable can be used to automatically update UI elements when the underlying data changes. Observables can also be used to manage asynchronous code, such as making AJAX requests or working with WebSockets.

11. Does RxJS support error handling for observables? If yes, then how does it work?

Yes, RxJS does support error handling for observables. There are a variety of ways to do this, but one way is to use the catch operator. This operator will catch any errors that occur in the observable sequence and allow you to handle them as you see fit.

12. Is there any way to make sure that subscriptions to observables are disposed properly when they’re no longer needed?

Yes, there are a few ways to do this. One way is to unsubscribe from the observable when it is no longer needed. Another way is to use the takeUntil operator, which will unsubscribe from an observable when another observable emits a value.

13. What happens if multiple subscribers subscribe to the same observable simultaneously?

If multiple subscribers subscribe to the same observable simultaneously, they will each receive the same emitted values. This is because observables are unicast, meaning that each subscriber receives its own independent stream of emitted values.

14. In your opinion, why should we use Observables over Promises?

Observables offer a number of advantages over Promises, including the ability to cancel requests, the ability to retry requests, and the ability to easily compose multiple Observables together.

15. What’s the best way to learn about and master observables?

The best way to learn about observables is to use them in your own code. Try to find places where observables would be a good fit, and then use them to build your own applications. As you use observables more and more, you will start to get a feel for how they work and how to use them effectively. There is no substitute for experience when it comes to mastering observables.

16. What is the role of the scheduler in context with an Observable?

The scheduler is responsible for managing the execution of an Observable. This includes ensuring that the Observable does not start executing until it is subscribed to, and that any unsubscribe callbacks are run when the subscription is disposed. The scheduler can also be used to control the concurrency of an Observable, which is important for ensuring that multiple subscribers do not cause side-effects.

17. What are the differences between promises and observables? When would you use one vs the other?

Promises are used when you need to handle a single async event, whereas observables are used when you need to handle multiple async events. Promises will emit a single value and then complete, whereas observables can emit multiple values over time. If you only need to handle a single async event, then a promise is probably all you need. If you need to handle multiple async events, then you will need to use an observable.

18. What are “cold” and “hot” observables?

“Cold” observables are those that begin emitting items only when they are subscribed to. “Hot” observables, on the other hand, begin emitting items as soon as they are created, regardless of whether or not they have any subscribers.

19. What is a Subject?

A Subject is an object that can both receive values from an Observable and emit values to an Observer. In this way, it can be thought of as both an Observer and an Observable. This makes it a very powerful tool in RxJS, as it can be used to multicast values to multiple Observers.

20. Can you explain what a multicast is?

A multicast is a way of sending a message to multiple recipients at the same time. This can be useful if you want to send a message to a group of people, or if you want to send the same message to multiple recipients.