Top 20+ Node JS Interview Questions and Answers

Q1. What is Node JS?

Node.js is a runtime environment that enables JavaScript to run on the server side using Chrome’s V8 engine. This is the most popular unified programming language for backend and frontend. This non-blocking architecture manages multiple existing connections. 

Q2. Why is Node JS more popular than other backend technologies like PHP and Java?

Some common reasons for popularity are;

• NPM ecosystem: Node Package Manager offers 50,000+ bundles to assist developers in boosting the development process.
• Unified codebase: One single code is used for both the client and server-side, boosting the synchronization process. 
• Fast performance: Node JS is popular for its speed handling for input output tasks. 
• Microservices Architecture Support: Node JS supports scalable and lightweight microservices with faster API integration. 
• Real-time applications: It manages real-time features, including live updates and chats, with its performance-driven architecture. 

Q3. What is NPM?

NPM refers to the Node Package Manager that manages each module and package for a Node JS. The key functions are;

• Online package management and installation: NPM has a central repository to install, update, and remove external code libraries. 
• Publishing and code sharing: It enables developers to publish, share, and reuse open-source libraries easily. 
• Common-line utility: It offers command-line tools to download, update, and handle project dependencies. 
• Security Auditing: NPM identifies issues in packages and boosts the application security.

Q4. How to handle errors in asynchronous code with a callback function?

You must pass an error object as the first parameter to handle the Errors in the callback. If an error happens, the callback returns it immediately; otherwise, it proceeds with the outcome. This is referred to as the Error-first callback pattern. 

Q5. What are the two API functions of Node JS? 

The two API functions of Node JS are;

• Asynchronous Functions: This is the non-blocking function best for performance. 
• Synchronous Functions: This is the blocking function best for task simplification. 

Q6. What do you mean by Control Flow in Node JS?

Control flow is the order in which asynchronous operations are performed. As Node JS is event-driven and non-blocking, tasks never finish as per order. Control flow manages the promises, async, and callbacks to manage the correct order of execution. 

Q7. How do you import a module in Node JS?

The “require” module is used to import the external resources in Node JS. The returned result is stored in a variable using require(). 

There are two different ways to import modules, and they are;

• ES Module (modern)

js

Import fs from ‘fs’;

• CommonJS (default)

js

Const fs = require(‘fs’);

Q8. What are REST APIs?

REST APIs are an architectural style that helps in communication between the backend and the frontend with the help of HTTP methods like DELETE, POST, GET, and PUT. 

Q9. What is the purpose of a V8 engine in Node JS?

The major purpose of a V8 engine is to compile JavaScript code into machine code. This makes the execution process faster. This is a Google-made engine and plays a major role in Node JS performance. 

Q10. What is the purpose of the package.json file?

The key purpose of the package.json file is to store dependencies, project metadata, version information, configurations, and scripts to handle Node.js applications easily. 

Q11. What is REPL? 

REPL in Node JS refers to Read, Eval, Print, Loop. This computing environment is similar to a shell, which is best for writing and executing code for testing and debugging. 

Q12. What is the use of “require” keyword in Node JS?

“require” in Node JS is used for importing modules in Node JS. It is also responsible for importing core Node JS libraries and JSON files into a well-performing web application. 

Q13. What are the differences between Synchronous and Asynchronous functions?

• Asynchronous Functions: This is the non-blocking function best for performance. It also boosts scalability. Handling errors is tough here, due to the presence of callbacks, promises, and async syntax.
• Synchronous Functions: This is the blocking function best for task simplification. Errors are easily caught using try-catch blocks. 

Q14. Why is Node JS single-threaded?

Node JS is a single-threaded event loop that handles multiple requests simultaneously. This helps reduce memory usage, complexity, and context switching, making applications more scalable and faster. 

Q15. What is a callback in Node JS?

A callback in Node JS refers to the function that is executed when an argument is passed to another function, and an asynchronous task is completed. 

Q16. How to create a web server using an in-built HTTP module?

Steps are;

• Importing the in-built ‘http’ module using ‘require()’
• Then use ‘http.createServer()’ and handle client responses and requests
• Response using ‘res.end()’ or ‘res.write()’ 
• Allocate a port number using ‘server.listen()’
• Running the file and assessing the server with ‘localhost’

Q17. What is event-driven programming?

Event-driven programming refers to executing code as a response to various events like API calls, messages, and actions. This model is highly used for non-blocking tasks. 

Q18. What are the different streams in Node JS?

The different streams in Node JS are;

• Readable stream to read data.
• Writable stream is to write data.
• Duplex stream is for supporting both the reading and writing tasks easily.
• The transfer stream is for processing data that changes the output as per the input.

Q19. What are LTS releases of Node JS? 

LTS refers to Long Term Support in Node JS fixes bugs, does security updates, and improves overall performance. The changes in the LTS version focus on NPM updates, performance updates, documentation improvements, bug fixes, and security patches. 

Q20. What is a test pyramid?

The test pyramid refers to the strategy that offers structured tests in a software project to ensure maintainability, effectiveness, and better coverage. Three levels of the test pyramid are Unit Tests (base), Integration Tests (Middle), and End-to-end Tests (Top). 

Q21. What are Promises?

Promises refer to objects that reflect the eventual failure or completion of an asynchronous task. It addresses callback hell by offering a cleaner and more readable way to collect async operations. 

Q22. What is Non-blocking and Blocking code in Node JS?

Blocking Codes execute the continuation and usage of a callback right after the task is complete. On the other hand, Non-blocking Codes stop the execution process till the task is done.