Top Node.js Interview Questions and Answers


Top Node.js Interview Questions and Answers :-

Here is the list of latest and updated Top Node.js Interview questions and answers for freshers as well as experienced users. so please take a look below :-

Q1. What is Node.js? Where can you use it?

Ans: Node.js is a server side scripting based on Google’s V8 JavaScript engine. It is used to build scalable programs especially web applications that are computationally simple but are frequently accessed.

You can use Node.js in developing I/O intensive web applications like video streaming sites. You can also use it for developing: Real-time web applications, Network applications, General-purpose applications and Distributed systems.

Q2. Why use Node.js?

Ans: Node.js makes building scalable network programs easy. Some of its advantages include:

  • It is generally fast
  • It almost never blocks
  • It offers a unified programming language and data type
  • Everything is asynchronous
  • It yields great concurrency

Q3. What are the features of Node.js?

Ans: Node.js is a single-threaded but highly scalable system that utilizes JavaScript as its scripting language. It uses asynchronous, event-driven I/O instead of separate processes or threads. It is able to achieve high output via single-threaded event loop and non-blocking I/O.

Q4. What is REPL in context of Node?

Ans: REPL stands for Read Eval Print Loop and it represents a computer environment like a window console or unix/linux shell where a command is entered and system responds with an output. Node.js or Node comes bundled with a REPL environment. It performs the following desired tasks.

  • Read – Reads user’s input, parse the input into JavaScript data-structure and stores in memory.
  • Eval – Takes and evaluates the data structure
  • Print – Prints the result
  • Loop – Loops the above command until user press ctrl-c twice.

Q5. What is global installation of dependencies?

Ans: Globally installed packages/dependencies are stored in <user-directory>/npm directory. Such dependencies can be used in CLI (Command Line Interface) function of any node.js but can not be imported using require() in Node application directly. To install a Node project globally use -g flag.

C:\Nodejs_WorkSpace>npm install express -g

Q6. What do you mean by the term I/O ?

Ans: I/O is the shorthand for input and output, and it will access anything outside of your application. It will be loaded into the machine memory to run the program, once the application is started.

Q7. Where can we use node.js?

Ans: Node.js can be used for the following purposes

a) Web applications ( especially real-time web apps )

b) Network applications

c) Distributed systems

d) General purpose applications

Q8. What are the two types of API functions in Node.js ?

Ans: The two types of API functions in Node.js are

a) Asynchronous, non-blocking functions

b) Synchronous, blocking functions

Q9. Why Node.js is single threaded ?

Ans: For async processing, Node.js was created explicitly as an experiment. It is believed that more performance and scalability can be achieved by doing async processing on a single thread under typical web loads than the typical thread based implementation.

Q10. Mention the steps by which you can async in Node.js ?

Ans: By following steps you can async Node.js

a) First class functions

b) Function composition

c) Callback Counters

d) Event loops

Q11. What is the difference between Node.js vs Ajax ?

Ans: The difference between Node.js and Ajax is that, Ajax (short for Asynchronous Javascript and XML) is a client side technology, often used for updating the contents of the page without refreshing it. While,Node.js is Server Side Javascript, used for developing server software. Node.js does not execute in the browser but by the server.

Q12. What does it mean “non-blocking” in node.js ?

Ans: In node.js “non-blocking” means that its IO is non-blocking.  Node uses “libuv” to handle its IO in a platform-agnostic way. On windows, it uses completion ports for unix it uses epoll or kqueue etc. So, it makes a non-blocking request and upon a request, it queues it within the event loop which call the JavaScript ‘callback’ on the main JavaScript thread.

Q13. What is ‘Callback’ in node.js ?

Ans: Callback function is used in node.js to deal with multiple requests made to the server. Like if you have a large file which is going to take a long time for a server to read and if you don’t want a server to get engage in reading that large file while dealing with other requests, call back function is used. Call back function allows the server to deal with pending request first and call a function when it is finished.

Q14. What is NPM ?

Ans: Node Package Manager. It is used to provide command line environment to install and manage NodeJS Packages, and NodeJS repositories that can be accessed at

Q15. What is the latest version of Node JS ?

Ans: Node v8.0.0 is the current version.

Q16. NodeJS is a framework. True or False.

Ans: False. It is runtime or environment, but not a framework.

Q17. What are event emitters in NodeJS?

Ans: Objects in NodeJS will have to trigger events in order to maintain asynchronous execution of core API used. These objects that emit events are known as Event Emitters.

Q18. List the tools and IDEs that are used for Node.js.


  • Atom
  • Nodeclipse Enide Studio
  • JetBrains WebStorm
  • JetBrains InteliJ IDEA
  • MS Visual Studio
  • NoFLo

Q19. Explain the role of the Callback function in Node.js.

Ans: In Node.js, the Callback function is used to cater to multiple requests made to the server. If there is a large file that is expected to take the server a long time to process, the Callback function can be invoked to ensure that other requests to the server are uninterrupted.

Q20. What is an error-first callback?

Ans: Error-first callbacks are essentially used to pass errors and data. By default, the first argument is always an error object, where the user needs to check if something is wrong.

Q21. List some of the big advantages of using Node.js.


  • Ability to build scalable programs
  • Increased concurrency
  • Asynchronous capabilities

Q22. Explain the Control Flow function.

Ans: It is a generic piece of code that runs concurrently between several asynchronous function calls.

Q23. List the steps involved in the Control Flow function.

Ans: Control the order of execution à Collect data à Limit concurrency à Call the next program step

Q24. Can a user access DOM in a Node?

Ans: No, you cannot access DOM.

Q25. In Node.js, how do you access the last expression?

Ans: We have to use the underscore (_) character to access the last expression.

Q26. In Node.js, which command is used to import external libraries?

Ans: A command called “require” is used for importing external libraries.

Q27. What is the biggest drawback of Node.js?

Ans: The biggest drawback is the fact that it is challenging to have one process with a single thread to scale up on multi core servers.

Q28. What are “streams” in Node.js? Explain the different types of streams present in Node.js.

Ans: Streams are objects that allow reading of data from the source and writing of data to the destination as a continuous process.

There are four types of streams.

  •   to facilitate the reading operation
  • to facilitate the writing operation
  • to facilitate both read and write operations
  • is a form of Duplex stream that performs computations based on the available input

Q29. What are exit codes in Node.js? List some exit codes.

Ans: Exit codes are specific codes that are used to end a “process” (a global object used to represent a node process).

Examples of exit codes include:

  • Unused
  • Uncaught Fatal Exception
  • Fatal Error
  • Non-function Internal Exception Handler
  • Internal Exception handler Run-Time Failure
  • Internal JavaScript Evaluation Failure

Q30. Why is consistent style important and what tools can be used to assure it?

Ans: Consistent style helps team members modify projects easily without having to get used to a new style every time. Tools that can help include Standard and ESLint.

So here we read about “Top Node.js Interview questions and answers”.

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