JavaScript and Node.js Interview Questions (Fresher)

Top 30+ JavaScript and Node.js Interview Questions for Freshers with Answers

If you’re preparing for your first job in tech, this is the place to start. These JavaScript and Node.js interview questions for freshers offer a structured way to master the basics. In fact, this guide helps entry-level developers succeed in interviews by covering easy, medium, and advanced topics for both technologies.

Easy JavaScript and Node.js Interview Questions for Freshers

1. What is JavaScript, and how is it different from Java?

JavaScript runs in the browser and handles client-side logic for interactive web pages. On the other hand, Java runs on virtual machines and supports general-purpose applications. Although they share a similar name, their roles differ greatly.

2. What are the basic data types in JavaScript?

JavaScript supports primitive types such as string, number, boolean, null, undefined, and symbol. Developers also use objects and arrays for complex data.

3. What is the difference between var, let, and const?

var defines function-scoped variables. let and const offer block-level scope. While let allows reassignment, const creates read-only variables.

4. What does hoisting mean in JavaScript?

JavaScript moves declarations to the top of their scope during compilation. This means you can use functions and variables before declaring them—but only the declarations, not the assignments.

5. How do you define a function in JavaScript?

Developers create functions using the function keyword, arrow functions, or expressions. For example: function greet() { return "Hi"; }

6. What is a closure?

A closure lets a function remember its lexical scope, even after the outer function finishes execution. This allows data to persist and remain private.

7. What are template literals?

Template literals use backticks and allow embedded variables with ${}. This makes string formatting easier and supports multiline strings.

8. What is the DOM?

The DOM, or Document Object Model, represents HTML elements as a tree structure. JavaScript uses it to read and change content, structure, and styles on web pages.

9. What does event bubbling mean?

When you trigger an event on a child element, it bubbles up to its parent elements. Developers can stop this by calling event.stopPropagation().

10. How does == differ from === in JavaScript?

== compares values after type conversion, while === compares both type and value. Developers prefer === for accurate comparisons.

Medium JavaScript and Node.js Interview Questions for Freshers

11. What is Node.js, and why do developers use it?

Node.js lets developers run JavaScript on the server. It handles concurrent requests efficiently using a non-blocking I/O model.

12. What does npm do?

npm (Node Package Manager) lets you install, update, and manage packages. Developers rely on it to add third-party libraries and tools to their Node.js projects.

13. What is a callback function?

A callback is a function you pass into another function to run later. JavaScript often uses them in asynchronous operations like file handling or API calls.

14. What is a Promise?

A Promise represents a value that may be available now, later, or never. It simplifies chaining asynchronous operations using .then() and .catch().

15. What is async/await?

These keywords allow you to write asynchronous code in a synchronous style. This makes your code easier to understand and debug.

16. What is Express.js?

Express.js is a web framework for Node.js. It helps developers create RESTful APIs and web apps with simple routing and middleware support.

17. How do you create an HTTP server in Node.js?

You can use Node’s http module:

const http = require('http');
http.createServer((req, res) => {
  res.end('Hello World');
}).listen(3000);

18. How does the event loop work in Node.js?

The event loop handles asynchronous tasks by checking the call stack and callback queue. It ensures non-blocking execution for I/O operations.

19. What is middleware in Express.js?

Middleware functions run between the request and response cycle. You can use them to log activity, authenticate users, or handle errors.

20. How do you handle CORS in Node.js?

CORS (Cross-Origin Resource Sharing) allows or restricts requests between different origins. In Express, you can handle it with the cors package.

Advanced Interview Questions for Freshers

21. What are streams in Node.js?

Streams let you process data in chunks instead of loading it all at once. Developers often use them for large file processing or real-time data.

22. How do you handle errors in Express.js?

You define an error-handling middleware with four parameters: err, req, res, next. It captures and responds to runtime errors.

23. How does asynchronous code differ from synchronous code?

Asynchronous code runs in the background, allowing other tasks to continue. Synchronous code, however, blocks further execution until it completes.

24. Why do developers use environment variables?

Environment variables store configuration values securely outside your codebase. They’re useful for things like API keys and database credentials.

25. How can you improve performance in a Node.js application?

Developers improve performance by using asynchronous code, caching responses, optimizing queries, and enabling clustering for multi-core usage.

26. What does clustering do in Node.js?

Clustering lets your application use multiple CPU cores. It launches child processes to handle concurrent requests, boosting performance.

27. What are some popular ES6 features?

ES6 introduced arrow functions, template literals, destructuring, classes, modules, and Promises—features that make your code cleaner and more powerful.

28. What is a module in Node.js?

A module is a file containing JavaScript code you can reuse elsewhere. Use module.exports to expose and require() to import them.

29. What is a buffer in Node.js?

A buffer holds raw binary data. Node uses it when reading files or handling TCP streams for fast and efficient processing.

30. How do you connect Node.js to a database?

You can use libraries like mongoose for MongoDB or sequelize for SQL. They simplify data models and support async CRUD operations.

Conclusion

In conclusion, practicing these JavaScript and Node.js interview questions for freshers boosts your confidence and prepares you for real-world challenges. Keep building small apps and solving problems to improve your understanding.