Node JS Interview Questions Advanced Level

1. What are Promises in Node.js?

Promises are objects that represent the eventual completion (or failure) of an asynchronous operation and its resulting value. They provide a cleaner alternative to callbacks, allowing for better handling of asynchronous code through .then() and .catch() methods.

2. What is a callback in Node.js, and how does it work?

A callback is a function passed as an argument to another function, which is executed after the completion of the asynchronous operation. This pattern allows for the execution of code after a task is completed, enabling asynchronous behavior.

3. What is the difference between process.nextTick() and setImmediate()?

process.nextTick() queues a callback to be invoked in the same phase of the event loop, before any I/O tasks. setImmediate() schedules a callback to be executed in the next iteration of the event loop after I/O events, making it useful for deferring execution until the current phase is complete.

4. Explain the concept of middleware in Express.js.

Middleware functions in Express.js are functions that have access to the request object (req), response object (res), and the next middleware function in the application’s request-response cycle. They can perform tasks like logging, authentication, and modifying the request/response objects. Middleware can be applied globally or to specific routes.

5. How do promises differ from callbacks?

Promises are objects representing the eventual completion (or failure) of an asynchronous operation. They provide a cleaner way to handle asynchronous operations compared to callbacks by avoiding “callback hell.” Promises can be in three states: pending, fulfilled, or rejected.

6. Explain how you can read a file in Node.js.

const fs = require(‘fs’); fs.readFile(‘example.txt’, ‘utf8’, (err, data) => { if (err) { console.error(err); return; } console.log(data); });

7. What are the differences between process.nextTick() and setImmediate()?

process.nextTick() queues a callback function to be executed after the current operation completes but before any I/O tasks. In contrast, setImmediate() schedules a callback to run after the I/O events in the current event loop iteration. This means process.nextTick() runs before setImmediate().

8. What is the purpose of the cluster module in Node.js?

The cluster module allows Node.js to create multiple child processes (workers) that share the same server port. This enables the application to take advantage of multi-core systems, improving performance and fault tolerance.

9. How do you create a RESTful API in Node.js?

10. What is the role of the package.json file?

The package.json file is a crucial component of a Node.js project that holds metadata about the project, including its name, version, dependencies, scripts, and other configurations. It allows npm to manage the packages used in the project.

11. What are the advantages of using Node.js for web development?

Node.js offers several advantages, including:

Non-blocking I/O: Enables handling multiple requests simultaneously.
Single Language: Uses JavaScript for both front-end and back-end development.
Performance: Built on the V8 engine, providing high performance for I/O-heavy applications.
Large Ecosystem: A vast number of libraries and packages available via npm.

12. What is the difference between require() and import in Node.js?

require() is the CommonJS module syntax used in Node.js for importing modules. It is synchronous and supports dynamic loading. import is part of the ES6 module syntax and is asynchronous. It allows for better optimization by supporting static analysis and tree shaking. Node.js supports both, but ES6 modules require a specific configuration.

13. Explain the significance of async and await.

async and await are syntactic sugar built on top of Promises, making asynchronous code easier to read and write. An async function always returns a Promise, and the await keyword pauses the execution of the function until the Promise is resolved or rejected.

14. What is the difference between a shallow copy and a deep copy?

A shallow copy creates a new object that references the same memory as the original object’s properties, meaning changes to nested objects will reflect in both. A deep copy creates a completely independent copy of an object and its nested objects, ensuring changes do not affect the original object. In Node.js, deep copies can be created using libraries like Lodash or by using structured cloning.

15. What are the different types of modules in Node.js?

Node.js primarily uses CommonJS modules, which export objects or functions using module.exports and import them with require(). ES6 modules, introduced in modern JavaScript, use export and import statements. There are also native modules, which are built into Node.js (like fs, http, etc.).

16. How do you handle uncaught exceptions in Node.js?

Uncaught exceptions can be handled using the process object. The process.on(‘uncaughtException’, callback) event can be used to log the error and perform cleanup before the application crashes. However, it’s best practice to handle errors at the point of failure and avoid relying on this method for managing critical errors.

17. What is the difference between Buffer and Stream in Node.js?

Buffer is a global object used to handle binary data directly in Node.js. It is useful for reading binary files or data from network sockets. Stream, on the other hand, is an abstract interface for working with streaming data, allowing you to read and write data continuously without loading the entire dataset into memory.

18. What is the purpose of the http module in Node.js?

The http module in Node.js allows developers to create HTTP servers and clients. It provides methods to handle HTTP requests and responses, making it easier to build web applications and APIs.

19. Explain the concept of CORS and how to enable it in Node.js.

Cross-Origin Resource Sharing (CORS) is a security feature that allows or restricts resources requested from a domain outside the domain from which the resource originated. In Node.js, CORS can be enabled using the cors middleware package, allowing you to specify which domains can access your resources.

20. How do you manage environment variables in a Node.js application?
Environment variables in Node.js can be managed using the process.env object. It’s common to use the dotenv package to load environment variables from a .env file into process.env, allowing for easy configuration management across different environments (development, testing, production).

21. What are the different ways to create a server in Node.js?

There are several ways to create a server in Node.js:

Using the built-in http module.
Using frameworks like Express.js for a more robust solution.
Using libraries like Koa or Hapi for specific features or improvements.

22. What are the common performance bottlenecks in Node.js applications?

Common performance bottlenecks include:

Blocking I/O operations (e.g., synchronous file reads/writes).
Excessive event listeners that consume memory.
High CPU-intensive tasks blocking the Event Loop.
Memory leaks due to unhandled closures or global variables.

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Node JS Interview Questions Advanced Level