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RxJS Interview Questions and Answers

RxJS Interview Questions and Answers

Question - 1 : - What is RxJS? / What do you understand by RxJS?

Answer - 1 : -

RxJS is an acronym that full form is Reactive Extension for Javascript. It is a JavaScript library that uses observables to work with reactive programming and deals with asynchronous data calls, callbacks and event-based programs. RxJS has introduced the concept of "reactive programming" to the web. It implements a reactive extension for TypeScript and JavaScript.

RxJS works as a combination of the observer pattern, iterator pattern and functional programming.

RxJS is a library for reactive programming using Observables to make it easier to compose asynchronous or callback-based code. It is a standalone JavaScript library that gives access to programmers to the Observable.
RxJS can also be used with other JavaScript libraries and frameworks. JavaScript and TypeScript well support it.

Question - 2 : - What is Reactive Programming?

Answer - 2 : -

Reactive programming is a declarative programming paradigm which deals with asynchronous data streams. Glenn Wadden first developed reactive programming in 1986 as a programming language in the Supervisory Control and Data Acquisition (SCADA) industry. Event buses or typical click events are called asynchronous event streams, used in reactive programming to observe and do some side effects. Reactive programming facilitates us to create data streams of anything, not just from click and hover events.

Question - 3 : - What should we know before going to learn RxJS?

Answer - 3 : -

Before learning RxJS, we must have a basic knowledge of JavaScript, JavaScript frameworks, and Angular. You can easily understand this technology if you have a basic understanding of JS.

Question - 4 : - What are the most outstanding features of RxJS?

Answer - 4 : -

Following is the list of some most important features of RxJS that are used to handle the concept of RxJS or reactive programming:


The Observer is an object with next(), error(), and complete() methods, which are called when we have to interact with the observable, i.e., the source interacts for an example button click, Http request, etc.


In RxJS, an observable function is used to create an observer and attaches it to the source where values are expected. For example, clicks, mouse events from a DOM element or an Http request, etc.

The role of subscription comes in the scene when the observable is created. To execute the observable, we need to subscribe to it. It can also be used to cancel the execution.


Operators are a very important part of RxJS. An operator is a pure function that takes observable input and emits the result in the output form. Input and output both are observable.

A subject is observable that can multicast, i.e., talk to many observers. Suppose we have a button with an event listener. The function attached to the event using addlistener is called every time the user clicks on the button. Similar functionality goes for the subject too.


A scheduler controls the execution of when the subscription has to start and be notified.

Question - 5 : - What are the biggest advantages of Reactive Programming?

Answer - 5 : -

Advantages of using Reactive Programming

  • Reactive programming provides a lot of operators that can simplify our work.
  • Reactive programming is very simple to compose streams of data.
  • It can be used to avoid "callback problems".
  • In Reactive programming, it is very simple to do async and threaded task.
  • It makes complex threading very easy.
  • By using Reactive programming, we can get a more cleaner and readable code base.
  • In Reactive programming, it is easy to implement back-pressure.

Question - 6 : - What are the biggest advantages and disadvantages of using RxJS?

Answer - 6 : -

Advantages of using RxJS
Following is the list of key advantages of using RxJS:

  • RxJS can be used with other Javascript libraries and frameworks. It is supported by javascript and also with typescript. Few examples are Angular, ReactJS, Vuejs, nodejs etc.
  • RxJS is an awesome library when it comes to the handling of async tasks. RxJS uses observables to work with reactive programming that deals with asynchronous data calls, callbacks and event-based programs.
  • RxJS offers a huge collection of operators in mathematical, transformation, filtering, utility, conditional, error handling, join categories that makes life easy when used with reactive programming.
Disadvantages of using RxJS
Following is the list of the biggest disadvantages of using RxJS:

  • Debugging the code with observables is a little difficult.
  • As you start to use Observables, you can end up with your full code wrapped under the observables.

Question - 7 : - What is Redux?

Answer - 7 : -

Redux is an open-source JavaScript library which is used to manage the application state. It is most commonly used with libraries such as React, Angular, or RxJS for building user interfaces. Redux is inspired by Facebook's Flux architecture and also very similar to it. It was created by Dan Abramov and Andrew Clark.

Question - 8 : - What are the core principles of Redux?

Answer - 8 : -

Redux follows the following three fundamental principles:

  • Single source of truth: It stores the state of your whole application in an object tree within a single store. The single state tree makes it easier to keep track of changes over time and debug or inspect the application.
  • State is ready only: It emits an action that is the only way to change the state. It ensures and specifies that neither the views nor the network callbacks will ever write directly to the state.
  • Changes are made with pure functions: We have to write pure reducers to specify how the state tree is transformed by actions. Reducers are simple pure functions that take the previous state and an action, and return the next state.

Question - 9 : - What do you understand by RxJS Stream?

Answer - 9 : -

An RxJS stream is a sequence of ongoing events ordered in time. In other words we can say that a stream is a sequence of data elements made available over time. A stream can be thought of as items on a conveyor belt being processed one at a time rather than in large batches. It is called stream because it acts as a data that is continuous and not really having an end, unless you explicitly define an end.

A stream can emit three different things:

  • a value (of some type)
  • an error
  • a "completed" signal

Question - 10 : - What do you understand by the Reactive Manifesto document?

Answer - 10 : -

A document was introduced to define the core principles of reactive programming. That document is known as the Reactive Manifesto. The Reactive Manifesto document was first released in 2013 by a group of developers led by a man called Jonas Boner. The Reactive Manifesto underpins the principles of reactive programming.

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