RxJS Interview Questions and Answers
Question - 11 : - Is there any similarity between Redux and RxJS?
Answer - 11 : -
Although Redux and RxJS are very different libraries for very different purposes, but they have some similarity also.
| Redux | RxJS |
| Redux is a tool used to manage state throughout the application. It is usually used as architecture for UIs. Iyt can be used as an alternative to (half of) Angular. | RxJS is a reactive programming library. It is usually used as a tool to accomplish asynchronous tasks in JavaScript. Think of it as an alternative to Promises. |
| Redux uses the Reactive paradigm little bit because the Store is reactive. The Store observes actions from a distance, and changes itself. | RxJS also uses the Reactive paradigm, but instead of being architecture, it gives you basic building blocks, Observables, to accomplish this "observing from a distance" pattern. |
Answer - 12 : -
In Reactive Programming, observables emit data, and send it to the subscribers. This process can be called as data being PUSHed in reactive programming. On the other hand, data is being PULLed in imperative programming, where we explicitly request data (iterating over collection, requesting data from the DB, etc).
Question - 13 : - What is the difference between BehaviorSubject and Observable in RxJS?
Answer - 13 : -
The following table specifies the differences between BehaviourSubject and Observable in RxJS:
| Observable | BehaviourSubject |
| In RxJS, observable is stateless. | In RxJS, BehaviourSubject is stateful. |
| Observable creates copy of data. | BehaviourSubject shares data. |
| Observable is unidirectional in nature. | BehaviourSubject is bidirectional in nature. |
Answer - 14 : -
Operators are very important part of RxJS. An RxJS operator is a pure function that takes an observable as input and provides the output also in the form of observable. We have to use a pipe() method to work with operators.
Following is a list of most used operators in RxJS:
- Creation Operator
- Mathematical Operator
- Join Operator
- Transformation Operator
- Filtering Operator
- Utility Operator
- Conditional Operator
- Multicasting Operator
- Error handling Operator
Further, these operators are sub-divided in other types of operators.
Question - 15 : - What is an Observable in RxJS?
Answer - 15 : -
In RxJS, an observable is a function that is used to create an observer and attaches it to the source where values are expected from. For example, clicks, mouse events from a DOM element or an Http request, etc. afre the example of RxJS observable. Observable gives us the idea of an invokable collection of future values or events. It facilitates us to make asynchronous data streams using observable sequences or just called observables, too.
We have to follow the following three steps to complete the RxJS observable:
- Create Observable
- Subscribe Observable
- Execute Observable
Question - 16 : - What is the difference between RxJS Observables and Promises?
Answer - 16 : -
Following is the list of main differences between RxJS Observables and Promises:
| RxJS Observables | Promises |
| Observables are used to run asynchronously, and we get the return value multiple times. | Promises are used to run asynchronously, and we get the return value only once. |
| Observables are lazy. | Promises are not lazy. |
| Observables can be canceled. | Promises cannot be canceled. |
| Observables provide multiple future values. | Promises provide a single future value. |
Answer - 17 : -
In RxJS, an Observable has many advantages over Promises. The following list shows some of them:
- An observable is like a Stream. It is used to pass zero or more events where the callback is called for each event.
- Observable is always preferred over Promise because it provides all the features of Promise and more.
- By using an observable, we can handle single or multiple events.
- Observables are cancelable, so this is also an advantage over Promises.
- Observable allows lazy initialization.
- Observable allows formatting data.
- Observable provides operators like map, forEach, reduce etc.
Question - 18 : - What is the difference between React and RxJS?
Answer - 18 : -
React is an open-source JavaScript library that is used to provide a view for data rendered as hypertext markup language. On the other hand, RxJS stands for Reactive Extensions for JavaScript. It is considered a library for composing asynchronous programming in web development and event-based programs using observable sequences and LINQ-style query operators. Let's see the key differences between them.
Difference between React and RxJS
| React | RxJS |
| React is an open-source JavaScript library. | RxJS is a library for composing asynchronous programming. |
| By using React, we can easily create interactive UIs. | By using React, we can easily create/compose asynchronous or callback-based code. |
Question - 19 : - What do you understand by the term Non-Blocking in RxJS?
Answer - 19 : -
In RxJS or Reactive programming, an algorithm is called non-blocking if threads competing for a resource do not have their execution indefinitely postponed by mutual exclusion protecting that resource.
This concept is used in an API that allows access to the resource if available; otherwise, it immediately returns informing the caller that the resource is not currently available or the operation has been initiated and not yet completed. A non-blocking API to a resource allows the caller to do other work rather than be blocked waiting on the resource to become available. This may be complemented by allowing the client to register for getting notified when the resource is available or the operation has been completed.
Question - 20 : - What does Asynchronous means in the context of RxJS or Reactive programming?
Answer - 20 : -
According to the Oxford Dictionary, the term asynchronous can be defined as "not existing or occurring at the same time." In the context of Reactive programming, it means that the processing of a request occurs at an arbitrary point in time, sometime after it has been transmitted from client to service. The client cannot directly observe, or synchronize with, the execution that occurs within the service. Asynchronous is the antonym of synchronous processing, which implies that the client only resumes its execution once the service has processed the request.