Latest Top interview questions and answers for a Node JS developer for experienced and freshers, get ready to crack any interview.

Basics of Node.js interview question:

1. What is Node.js?
   • Answer: Node.js is a server-side JavaScript runtime built on the V8 JavaScript engine. It allows developers to run JavaScript code on the server, enabling the development of scalable and high-performance web applications.
2. Explain the event-driven architecture in Node.js.
   • Answer: Node.js is designed to be event-driven and non-blocking. It uses an event loop to handle events asynchronously, making it highly scalable for handling concurrent connections.
3. How do you handle asynchronous operations in Node.js?
   • Answer: Asynchronous operations in Node.js are handled using callbacks, Promises, or the async/await syntax. The event-driven architecture allows non-blocking I/O operations.
4. What is npm, and how is it used in Node.js?
   • Answer: npm (Node Package Manager) is the default package manager for Node.js. It is used to install, manage, and share JavaScript packages and libraries.
5. Explain the role of the require function in Node.js.
   • Answer: The require function is used to import modules in Node.js. It allows using code from other files by including the module’s exports.
6. What is the purpose of the fs module in Node.js?
   • Answer: The fs (File System) module in Node.js provides functions for interacting with the file system. It allows reading, writing, and manipulating files and directories.
7. How do you create a basic server in Node.js using the http module?
   • Answer: You can create a basic server using the http module by creating an instance of http.Server and listening for requests.

const http = require('http');
const server = http.createServer((req, res) => {
  res.end('Hello, World!');
});
server.listen(3000, () => console.log('Server running on port 3000'));

1. Explain the concept of middleware in Node.js.
   • Answer: Middleware in Node.js are functions that have access to the request, response, and the next middleware function. They can modify request or response objects, end the request-response cycle, or call the next middleware.
2. What is the purpose of the process object in Node.js?
   • Answer: The process object in Node.js provides information about the current Node.js process. It can be used to access command-line arguments, environment variables, and manage the process lifecycle.
3. What is the role of the Buffer class in Node.js?
   • Answer: The Buffer class in Node.js is used to handle binary data directly. It provides a way to work with raw binary data and is particularly useful for working with streams and file systems.

Advanced Node.js Concepts interview question:

11. Explain the concept of streams in Node.js.
    • Answer: Streams in Node.js are objects that allow reading or writing data sequentially. They help in efficiently processing large amounts of data by dividing it into smaller chunks.
12. What is the purpose of the events module in Node.js?
    • Answer: The events module in Node.js provides an EventEmitter class that allows the creation and handling of custom events. It is a fundamental part of the event-driven architecture in Node.js.
13. How does clustering work in Node.js, and why is it useful?
    • Answer: Clustering in Node.js involves creating multiple instances (workers) of the application to handle concurrent connections. It is useful for utilizing multiple CPU cores and improving performance.
14. Explain the concept of the Node.js event loop.
    • Answer: The event loop in Node.js is a continuous process that waits for events and executes callback functions when events occur. It allows non-blocking execution of code and efficient handling of I/O operations.
15. What is the purpose of the cluster module in Node.js?
    • Answer: The cluster module in Node.js allows the creation of child processes (workers) to distribute the load across multiple CPU cores. It helps in achieving better performance and scalability.
16. How does error handling work in Node.js?
    • Answer: Error handling in Node.js is typically done using try-catch blocks for synchronous code and callback functions with the first parameter as an error object for asynchronous code. Promises and the async/await syntax also provide ways to handle errors.
17. Explain the role of the util module in Node.js.
    • Answer: The util module in Node.js provides utility functions that are useful for debugging and working with objects. It includes functions like util.promisify for converting callback-based functions to Promises.
18. What is the purpose of the child_process module in Node.js?
    • Answer: The child_process module in Node.js allows the creation of child processes to run external commands or scripts. It is useful for tasks that require parallel or separate processing.
19. How does garbage collection work in Node.js?
    • Answer: Node.js uses the V8 JavaScript engine, which employs automatic garbage collection. Objects that are no longer referenced are automatically identified and reclaimed by the garbage collector.
20. Explain the concept of the Node.js module system.
    • Answer: The Node.js module system allows the organization of code into separate files (modules). Modules can export functionalities using module.exports and import functionalities using require.

Web Development with Node.js interview question:

21. How do you connect Node.js to a database like MongoDB?
    • Answer: You can connect Node.js to MongoDB using the official MongoDB Node.js driver or an Object Data Modeling (ODM) library like Mongoose.

const mongoose = require('mongoose');
mongoose.connect('mongodb://localhost:27017/database', { useNewUrlParser: true, useUnifiedTopology: true });

21. Explain the purpose of the Express.js framework.
    • Answer: Express.js is a web application framework for Node.js. It simplifies the process of building robust and scalable web applications by providing features like routing, middleware, and template engines.
22. How do you handle authentication in a Node.js application?
    • Answer: Authentication in Node.js can be implemented using libraries like Passport.js. It involves strategies for different authentication methods (e.g., local, OAuth), session management, and protecting routes.
23. What is WebSocket, and how is it implemented in Node.js?
    • Answer: WebSocket is a communication protocol that provides full-duplex communication channels over a single, long-lived connection. In Node.js, libraries like socket.io are commonly used to implement WebSocket functionality.
24. Explain the purpose of the cookie-parser middleware in Express.js.
    • Answer: The cookie-parser middleware in Express.js parses and handles cookies in HTTP requests. It facilitates working with cookies in a web application.

Testing in Node.js interview question:

26. How can you perform unit testing in Node.js?
    • Answer: Unit testing in Node.js can be performed using testing frameworks like Mocha or Jest. Assertions can be done using libraries like Chai or built-in assert module.
27. What is the purpose of the supertest library in Node.js testing?
    • Answer: The supertest library is used for testing HTTP assertions in Node.js applications. It allows making requests to the application and asserting the response.
28. How do you mock dependencies in Node.js testing?
    • Answer: Dependencies in Node.js testing can be mocked using tools like sinon or by creating manual mocks. Mocks help isolate the code under test and control the behavior of dependencies.
29. What is end-to-end testing, and how is it performed in Node.js applications?
    • Answer: End-to-end testing involves testing an application’s complete workflow. In Node.js, tools like Puppeteer or Cypress can be used for end-to-end testing.
30. Explain the concept of code coverage in Node.js testing.
    • Answer: Code coverage measures the percentage of code that is executed during testing. Tools like Istanbul or Jest provide code coverage reports to identify untested code.