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20 Frequently Asked Node.js Interview Questions and Answers

Node.js is recognized as a pioneering server-side technology. If you want to be an expert MEAN stack developer you need to master Node.js. This web development tool is not just highly remunerative but incredibly progressive with technological innovation.

In case you’ve got an upcoming interview or to be prepared for ones in the near future, the below-outlined 20 interview questions should assist you to an acceptable extent in preparing to answer correctly and confidently every question when asked.

List of Top 20 Node.js Interview Questions with answers

  • What is Node.js?
  • Where is Node.js used?
  • What benefits does Node.js offer?
  • What are the features of Node.js?
  • How do you define EventEmitter in Node.js?
  • Why is Node.js Single-threaded?
  • How to obtain a post data in Node.js?
  • How to create a post request in Node.js?
  • Explain REPL in Node.js.
  • What are the primary functions of NPM in Node.js?
  • What is the process to update NPM to a new Node.js version?
  • What is callback functionality in Node.js?
  • How does a callback hell happen in Node.js?
  • How can you prevent or rectify a callback hell?
  • Explain the difference between Node.js and Ajax?
  • Explain the process of chaining in Node.js?
  • What types of API functions are used in Node.js?
  • How do you define streams in Node.js? Elucidate the various types of streams?
  • What do you mean by Globals in Node.js?
  • What are exit codes in Node.js? Give some examples?

#1. What is Node.js?

Node.js is a scripting platform built on an engine supported by Google’s V8 JavaScript. The runtime of Node.js enables execution of the JavaScript code by any server outside the scope of a browser.

#2. Where is Node.js used?

The primary utilization of Node.js lies in building scalable programs. They are ideally web applications which can be easily computed and frequently accessed. It also finds application in the development of I/O intensive web applications. These include mainly sites that offer video streaming. Furthermore you can use Node.js to build

  • Real-time web applications
  • General-purpose applications
  • Network applications
  • Distributed systems

#3. What benefits does Node.js offer?

Node.js facilitates easy buildup of scalable programs for the network. Inherent advantages include:

  • Speedy functioning
  • Offers no blockage
  • Provides a unified programming language as well as data type
  • Asynchronous operation
  • Greater concurrency

#4. What are the features of Node.js?

Node.js has a single-threaded, yet highly scalable integration. Its scripting language is JavaScript. It makes use of asynchronous and event-driven I/O. It doesn’t support multiple threads or processes. It achieves high-yielding output by utilizing single-threaded event loop as well as non-blocking I/O.

#5. How do you define EventEmitter in Node.js?

Every object that emits events is an example of the EventEmitter category. This object is used in raising and handling custom events. The following code gives access to the EventEmitter.

An EventEmitter triggers the following events

  • “Error” when something erroneous is encountered
  • “NewListener” when a new listener is added
  • “RemoveListener” when a listener is removed.

EventEmitter bears innate properties like “On” and “emit”. The former attaches the event with a function. The latter fires an event.

$6. Why is Node.js Single-threaded?

To facilitate asynchronous processing Node.js is single-threaded. By doing so, heightened scalability and performance can be attained under typical web loads. The more habitual thread-based applications are less robust in these aspects.

#7. How to obtain a post data in Node.js?

In order to fetch post data using Node.js the following code is used.

#8. How to create a post request in Node.js?

You can make a post request by applying the below-mentioned code.

#9.  REPL in Node.js?

REPL is the abbreviation for Read-Eval-Print-Loop. It’s a collaborative Node.js virtual environment used to quickly test JavaScript codes. Some of the commonly used REPL commands are listed below.

#10. What are the primary functions of NPM in Node.js?

NPM (Node Package Manager) in Node.js has two principal functions.

  • Providing an online repository for Node.js packages
  • Offering a command line utility to install packages, manage versions and dependency of Node.js packages

#11. What is the process to update NPM to a new Node.js version?

The following command is used for a successful update.

#12. What is callback functionality in Node.js?

This function signifies the completion of an assigned task. It prevents code blocking. Meanwhile, it enables other codes to be processed. Because of its asynchronous nature Node.js depends majorly on callback facility. Every Node.js API is written in compatibility with callback.

#13. How does a callback hell happen in Node.js?

A callback hell takes a form when heavily nested callbacks are conceived. It not only makes the code illegible but also makes them hard to maintain. Given below is an example of callback hell.

#14. How can you prevent or rectify a callback hell?

There are four ways to do this.

  • Handling of every individual error
  • Keeping a shallow code structure
  • Creating and splitting callbacks into small modules. Each module functions independently. They are invoked with certain parameters and joined to obtain desired results.  
  • Utilizing generators, promises and asynchronous functions

The first level to improve a code is shown below.

#15. Explain the difference between Node.js and Ajax?

Node.js and Ajax (Asynchronous JavaScript and XML) are two advanced and grossly different JavaScript applications.

  • Node.js helps developing client-server applications.
  • Ajax performs dynamic update of a portion of a certain page content. It doesn’t update the whole page.

#16. Explain the process of chaining in Node.js?

Chaining is a specialized technique by virtue of which interconnection of several streams is put into operation. It creates an elaborate chain of multi-stream functionality.

#17. What types of API functions are used in Node.js?

The two primary functions in Node.js are as follows.

  • Blocking function

It blocks all other codes from being executed until the completion of the first I/O event put in queue. The execution of blocking function happens synchronously. Also the next line-up of codes blocks additional JavaScript execution until the reading of the whole file is finished.

  • Non-blocking function

This enables performance of many I/O calls without having to block or halt any program. Non-blocking function takes to asynchronous mode of operation.

#18. How do you define streams in Node.js? Elucidate the various types of streams.

Streams are unique objects that enable data capturing and reading from the source and subsequent data writing into the destination through a continual process.

Streams are categorized into four types depending on their function.

  • Facilitate data reading
  • Facilitate data writing
  • Facilitate both data reading and writing simultaneously
  • Facilitate duplex operation that also computes and executes contingent on the accessible input.

#19. What do you mean by Globals in Node.js?

In Node.js, there are three keywords that constitute Globals.

  • Global – Characterized by a Global namespace object it helps to hold and contain different objects.
  • Process – This keyword aids a synchronous function to change into an asynchronous callback. It has got a universal code access. It basically returns information related to either the environment or the environment.
  • Buffer – A specific class in Node.js used for the handling of binary data.

#20. What are exit codes in Node.js? Give some examples.

Exit codes are defined as specific codes that contribute to end a process which is primarily a global object meant for representing a node process.

Some of the most common exit codes are.

  • Unused
  • Fatal error
  • Uncaught fatal exception
  • Non-function internal exception handler
  • Internal JavaScript evaluation failure
  • Internal exception handler run-time failure

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