Top 20 Node.js Interview Questions and Answers

With the boosting popularity of JavaScript, the world has seen a revolutionary change in web development. The process and techniques of web designing have taken a dramatic turn. JavaScript running on the server and in the browser has opened new possibilities and helped us discover ways we weren’t aware of.

1. What is node.js? How node.js works?

Node.js is an open source, cross-platform runtime environment for developing server-side and networking applications written in JavaScript. It is the archetype of an exceedingly customizable and scalable tech. JS is designed to use single-threaded, event-based architecture and non-blocking based I/O models. It is made of Google Chrome’s V8 engine written in multiple-platform C library i.e C++ and Libuv that backs asynchronous I/O based events on event loops and thread loops. Although Node.js is made of Libuv, it can still be used in pure JavaScript.

2. Where can we use node.js?

Node.js can be used at a variety of platforms. Some examples are stated below:

• Backend for Social Media Networking – LinkedIn
• Single-page Application – GitHub
• Chat Application –
• Data Streaming – Netflix
• IoT Application – PREE

3. What is the advantage of using node.js?

Node.js is used by professionals and some extremely renowned companies like Netflix and Uber. Evidently, it possesses features that make it the best. Below mentioned are some advantages of using Node.js

• Easy to learn because of its accessibility and object-oriented programming.
• Simple to use because it only uses one language as the catalyst of the full-stack development.
• It is Faster to deploy, as programs and websites built with Node.js require less time on development hence reducing the overall time-to-market.
• Node.js is a scalable alternative to Apache. It can handle various concurrent connections and distribute tasks skillfully amongst resources.

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

Node.js has two types of API functions

• Asynchronous, Non-blocking functions
• Synchronous, Blocking functions

5. What is control flow function? Explain the steps how “Control Flow” controls the functions calls?

The order in which the execution of statements is done by the computer is called Control Flow. The control flow function in Node.js is a code that is applied between Asynchronous function calls. Below given are steps which are used to implement Control Flow Function.

• Execution order must be controlled
• Collect the required data
• Concurrency must be limited
• After this, the program is requested

6. Why is Node.js quickly gaining attention from JAVA programmers?

The reason behind Node.js rapidly gaining popularity is its loop-based server for JavaScript. Node.js provides the developer the facility to write JavaScript on the server.

7. What is the event loop in Node.js work? And how does it work?

The I/O non-blocking operation of Node.js is made possible through event loops despite JavaScript is a single-threaded language. At the beginning of the process, Node.js initialises the event loop, processes the provided input script that syncs API calls, schedule timers, then starts processing the event loops.

8. How will you debug an application in Node.js?

Debugging means relieving your code from any error. Identifying an error can take up many hours for which Node.js has a great tool that can help finding the error.

Open the initial file (typically index.js), activate the Run and Debug pane, and click the Run and Debug Node.js (F5) button. The debugging screen is similar to Chrome DevTools with a Variables, Watch, Call stack, Loaded scripts, and Breakpoints list.

9. What are some of the most popular modules of Node.js?

Every developer must be equipped with the latest information and updates on software libraries as they make the task of programming very easy. The most popular and useful modules of Node.js are-

• Express
• Socket.io
• Body-parser
• Cora
• Passport
• Multer

10. What is a Callback function in Node.js?

Callback function is employed when a task is complete. Hence it is a precaution against any kind of blocking. In the meantime, the callback function allows other codes to run. With the Callback function, Node.js becomes immensely scalable as it can process a large amount of requests without waiting for any function to return the results.

11. What are the challenges with Node.js?

Even though Node.js is one of the most popular and widely used open sources software, it has its own challenges-

• The performance of Node.js is restricted by the heavy computation tasks and also till date Node.js cannot process CPU bound tasks.
• There might be Callback issues because of their asynchronous nature.
• Despite having stable modules, Node.js still has immaturity within tools. There are several tools in the npm registry that aren’t structured well enough.

12. What is REPL in Node.js?

REPL stands for Read-Eval-Print-Loop. This is a virtual environment that comes with Node.js. It is a quick and easy way to test simple Node.js codes.

13. What is a test pyramid in Node.js?

A test pyramid is a metaphor that is used to make a bunch of software tests of different granularity. For example, unit testing, component testing, integration testing, system testing, end-to-end testing, UI testing.

14. Explain the concept of middleware in Node.js.

Middleware is a function that has the access to the requested object, requested response and the next function in the application’s request-response cycle. The middleware function can perform multiple tasks such as; execute code, make changes to the request and the response objects, end the request-response cycle and call the next middleware in the stack.

15. Describe Node.js exit codes.

Exit codes in Node.js are particular codes which help in finishing the processes. This may also include global objects. Some examples of exit code in Node.js are-

• Internal JavaScript Evaluation Failure
• Fatal Error
• Internal Exception
• Handler Run-time failure
• Unused
• Uncaught fatal exception

16. Differentiate between Node.js vs Ajax?

The major difference between Nodes.js and Ajax is –

Nodes.js is a server-side platform for developing client-server applications, whereas Ajax is a client-side scripting technique that was basically designed to show the contents of a page without refreshing it.

17. What are the security mechanisms available in Node.js?

Node.js is equipped with various security mechanism, some are mentioned below:

• Certified Security Modules can assess any third part codes that are catered into the software.
• Regular updates of versions are made in Node.js so that it does not become vulnerable to hackers.
• Curated Screening Register is a kind of quality control system through which every new package code or software is passed to maintain safety before downloading.

18. What are some of the flags used in the read/write operations in files?

Node.js uses several flags in the read/write operations in files. Below mentioned are some of the flags:

• r : open file for reading
• r+ : open file for reading and writing
• rs : Open file for reading in synchronous mode
• w : Open file for writing
• a : Open file for appending

19. What is the difference between fork() and spawn() methods in Node.js?

Spawn command is designed to run system commands. When Spawn command is used, you send it a system command that is processed on its own but no further code is processed within your node process. Whereas, Fork is a special instance of Spawn. This means that you can create workers for running the exact same Node code base or maybe a different module for a particular task.

20. What do you understand by an Event Emitter in Node.js?

Node.js is created with a feature of conducting custom events by using event modules. These event modules include an EventEmitter class that is used to raise and operate custom events. Some important methods of EventEmitter class are:

• emitter.addListener(event, listener)
• emitter.on(event, listener)
• emitter.once(event, listener)
• emitter.removeListener(event, listener)
• emitter.remove all listeners([event])