Node Interview Questions and Answers (2025) - Advanced Level

Last Updated : 26 Feb, 2025

NodeJS is an open-source and cross-platform runtime environment built on Chrome’s V8 JavaScript engine for executing JavaScript code outside of a browser. You need to recollect that NodeJS isn’t a framework, and it’s not a programming language. It provides an event-driven, non-blocking (asynchronous) I/O and cross-platform runtime environment for building highly scalable server-side applications using JavaScript.

In this article, you will learn NodeJS interview questions and answers - Advanced level 2025 that are most frequently asked in interviews. This will help you to ace Interviews having 2-3 years of experience and also help to grasp he advanced concepts of NodeJS even if you are beginner.

Prerequisites

Node Advanced Interview Questions - 2025

This set contains the advanced-level questions asked in the interview.

1. What is a cluster in NodeJS?

Due to a single thread in NodeJS, it handles memory more efficiently because there are no multiple threads due to which no thread management is needed. Now, to handle workload efficiently and to take advantage of computer multi-core systems, cluster modules are created that provide us the way to make child processes that run simultaneously with a single parent process.

2. Explain some of the cluster methods in NodeJS

Fork(): It creates a new child process from the master. The isMaster returns true if the current process is master or else false.
isWorker: It returns true if the current process is a worker or else false.
process: It returns the global child process.
send(): It sends a message from the worker to the master or vice versa.
kill(): It is used to kill the current worker.

3. How to manage sessions in NodeJS?

Session management can be done in NodeJS by using the express-session module. It helps in saving the data in the key-value form. In this module, the session data is not saved in the cookie itself, just the session ID.

4. Explain the types of streams in NodeJS

Types of Stream

Readable stream: It is the stream from where you can receive and read the data in an ordered fashion. However, you are not allowed to send anything. For example, fs.createReadStream() lets us read the contents of a file.
Writable stream: It is the stream where you can send data in an ordered fashion but you are not allowed to receive it back. For example, fs.createWriteStream() lets us write data to a file.
Duplex stream: It is the stream that is both readable and writable. Thus you can send in and receive data together. For example, net.Socket is a TCP socket.
Transform stream: It is the stream that is used to modify the data or transform it as it is read. The transform stream is basically a duplex in nature. For example, zlib.createGzip stream is used to compress the data using gzip.

5. Explain the concept of middleware in NodeJS.

In NodeJS, middleware refers to functions that are executed during the request-response cycle of an HTTP request. These functions can perform a variety of tasks such as modifying the request or response objects, handling errors, or terminating the request-response cycle.

6. Explain the packages used for file uploading in NodeJS?

The package used for file uploading in NodeJS is Multer. The file can be uploaded to the server using this module. There are other modules in the market but Multer is very popular when it comes to file uploading. Multer is a NodeJS middleware that is used for handling multipart/form-data, which is a mostly used library for uploading files.

7. Explain the difference between NodeJS and server-side scripting languages like Python

Features	NodeJS	Server-Side Scripting Languages (e.g., Python)
Platform	A runtime environment for executing JavaScript outside the browser.	A programming language that can be used for server-side scripting (e.g., Python, PHP, Ruby).
Language	Built on JavaScript, primarily used for asynchronous programming.	Built on Python, which is synchronous by default, but can also be used for asynchronous programming.
Concurrency Model	Non-blocking, event-driven I/O model using the Event Loop.	Thread-based concurrency (multi-threading) or asynchronous programming with frameworks like asyncio.
Performance	Highly performant for I/O-heavy tasks but less efficient for CPU-heavy operations due to single-threaded nature.	More suitable for CPU-heavy operations but can be less performant in handling high concurrency compared to NodeJS.
Use Case	Used for building fast, scalable, I/O-bound applications (e.g., APIs, real-time apps).	Commonly used for general-purpose programming, web development, and CPU-bound tasks (e.g., Django for web, machine learning with libraries like TensorFlow).

8. How to handle database connection in NodeJS?

To handle database connection in NodeJS we use the driver for MySQL and libraries like Mongoose for connecting to the MongoDB database. These libraries provide methods to connect to the database and execute queries.

9. How to read command line arguments in NodeJS?

Command-line arguments (CLI) are strings of text used to pass additional information to a program when an application is running through the command line interface of an operating system. We can easily read these arguments by the global object in node i.e. process object. Below is the approach:

Step 1: Save a file as index.js and paste the below code inside the file.

JavaScript

let arguments = process.argv ;

console.log(arguments) ;

Step 2: Run the index.js file using the below command:

node index.js

10. Explain the NodeJS redis module

Redis is an Open Source store for storing data structures. It is used in multiple ways. It is used as a database, cache, and message broker. It can store data structures such as strings, hashes, sets, sorted sets, bitmaps, indexes, and streams. Redis is very useful for NodeJS developers as it reduces the cache size which makes the application more efficient. However, it is very easy to integrate Redis with NodeJS applications.

11. What is web socket?

Web Socket is a protocol that provides full-duplex (multiway) communication i.e. allows communication in both directions simultaneously. Web Socket is a modern web technology in which there is a continuous connection between the user’s browser (client) and the server. In this type of communication, between the web server and the web browser, both of them can send messages to each other at any point in time.

12. Explain the util module in NodeJS

The Util module in NodeJS provides access to various utility functions. There are various utility modules available in the NodeJS module library.

OS Module: Operating System-based utility modules for NodeJS are provided by the OS module.
Path Module: The path module in NodeJS is used for transforming and handling various file paths.
DNS Module: DNS Module enables us to use the underlying Operating System name resolution functionalities. The actual DNS lookup is also performed by the DNS Module.
Net Module: Net Module in NodeJS is used for the creation of both client and server. Similar to DNS Module this module also provides an asynchronous network wrapper.

13. How to handle environment variables in NodeJS?

We use process.env to handle environment variables in NodeJS. We can specify environment configurations as well as keys in the .env file. To access the variable in the application, we use the "process.env.VARIABLE_NAME" syntax. To use it we have to install the dotenv package using the below command:

npm install dotenv

14. Explain DNS module in NodeJS

DNS is a node module used to do name resolution facility which is provided by the operating system as well as used to do an actual DNS lookup. Its main advantage is that there is no need for memorizing IP addresses – DNS servers provide a nifty solution for converting domain or subdomain names to IP addresses.

15. What are child processes in NodeJS?

Usually, NodeJS allows single-threaded, non-blocking performance but running a single thread in a CPU cannot handle increasing workload hence the child_process module can be used to spawn child processes. The child processes communicate with each other using a built-in messaging system.

16. How to validate data in NodeJS?

Validation in NodeJS can be easily done by using the express-validator module. This module is popular for data validation. There are other modules available in the market like hapi/joi, etc but express-validator is widely used and popular among them.

17. What is the role of net module in NodeJS?

The net module in NodeJS is used to create TCP client and serve in NodeJS. This module establishes connections, handles incoming requests, and share data over the network.

18. What is tracing in NodeJS?

The Tracing Objects are used for a set of categories to enable and disable the tracing. When tracing events are created then tracing objects is disabled by calling tracing.enable() method and then categories are added to the set of enabled trace and can be accessed by calling tracing.categories.

19. What is reactor pattern in NodeJS?

Reactor Pattern is used to avoid the blocking of the Input/Output operations. It provides us with a handler that is associated with I/O operations. When the I/O requests are to be generated, they get submitted to a demultiplexer, which handles concurrency in avoiding the blocking of the I/O mode and collects the requests in the form of an event and queues those events.

20. How to Connect NodeJS to a MongoDB Database?

To connect to MongoDB database write the following code after installing the Mongoose package:

JavaScript

const mongoose = require("mongoose");

mongoose.connect("DATABASE_URL_HERE", {
   useNewUrlParser: true,
   useUnifiedTopology: true
});

21. What is the difference between setImmediate() and setTimeout()?

Features	steImmediate()	setTimeout()
Execution Timing	Executes the callback immediately after the current event loop phase.	Executes the callback after the specified delay (in ms).
Callback Queue	Adds the callback to the next iteration of the event loop, in the check phase.	Adds the callback to the timer queue, to be executed after the specified delay.
Timer Resolution	Has no timer; it is designed for immediate execution.	Executes only after the specified delay, which may vary slightly based on system timing resolution.
Delay	No delay, always executes after the current phase finishes.	Executes after the specified delay (minimum of 1 ms).
Use Case	Used for callbacks that need to run immediately after I/O events or timers.	Used for delaying the execution of a callback by a specific time.

22. What are global objects in NodeJS?

Global objects in NodeJS are objects that are available in all modules without needing to be imported. These objects provide built-in functionalities and information about the NodeJS environment. They are similar to the window object in browsers but are tailored for server-side JavaScript.

23. How does NodeJS overcome the problem of blocking I/O operations?

By using an asynchronous, non-blocking I/O model, NodeJS overcome the problem of blocking I/O problems.

24. What is "non-blocking" in NodeJS?

In NodeJS non-blocking is the way in which the NodeJS handles the I/O operations (such as reading from a file, making HTTP requests, or querying a database) without blocking the execution of other code. It doesn't wait for the task to finish before moving on to the next line of code. Instead, it allows the next operations to execute, and once the I/O task is complete, it triggers a callback to handle the result.

25. For NodeJS, why does Google use the V8 engine?

Google use the V8 engine for the NodeJS of the following reasons mentioned below:

High Performance: V8 is a highly optimized JavaScript engine designed for speed. It compiles JavaScript directly into machine code, which makes it much faster than interpreted JavaScript.
Just-In-Time (JIT) Compilation: V8 uses JIT compilation, which translates JavaScript code into machine code during execution, enabling faster execution compared to traditional interpretation.
Cross-platform Compatibility: V8 is cross-platform due to which the NodeJS application can run on the different platforms.
Integration with Google Chrome: V8 is the engine which is used in the Google Chrome by using the V8 engine in the NodeJS ensures consistency in performance and features.
Asynchronous I/O Efficiency: V8 engine can handles the non-blocking, asynchronous I/O operations which is important for handling the multiple tasks in NodeJS.

26. What is a test pyramid in NodeJS?

In the NodeJS environment testing pyramid is the conceptual model which guides the developers in structuring their test suites. The test pyramid mainly consist of the three main parts:

Unit Tests (Base of the Pyramid): Testing individual units of code (e.g., functions, methods, or small components).
Integration Tests (Middle of the Pyramid): Testing how multiple components work together, such as how a function interacts with a database or an API.
End-to-End (E2E) Tests (Top of the Pyramid): Testing the application as a whole, simulating real user behavior across various parts of the system.

27. What is piping in NodeJS?

In NodeJS piping can be defined as the mechanism in which we can use the output of one stream to the input of the other stream. When we deal with the large data then piping simplifies the process of the handling data streams by automatically managing the data flow. This can be achieved using the pipe() method which is available on readable streams.

28. What is REPL in NodeJS?

In NodeJS REPL stands for the Read-Evaluate-Print-Loop. REPL read the input evaluate it prints the result and then loop back again to read the next input and this continue until unless the user do not exits. node command in run in the terminal for starting the repel.

Read: Read is used to read the user input and then parse the input into the JavaScript and stores it in the memory.
Eval: It takes the input and evaluates the data structure.
Print: It is used to print the result.
Loop: It is used to loop again until user exits.

29. What is the buffer class in NodeJS?

The Buffer class in NodeJS provides a way to handle binary data. It represents a fixed-size chunk of memory, similar to an array of integers, but outside the V8 heap. Buffers are important because JavaScript traditionally lacks mechanisms for directly manipulating binary data streams. Buffers cab be used in various scenarios, such as when reading from or writing to files, handling network streams, or working with binary data formats.

30. What is the difference between fork() and spawn() methods in NodeJS?

Features	fork()	spawn()
Purpose	Used to create a new NodeJS process that runs a separate JavaScript file.	Used to launch a new child process to execute a command in the shell.
IPC (Inter-process Communication)	Built-in IPC support for communication between parent and child processes.	No built-in IPC; communication is done via standard input/output (stdin, stdout).
Arguments	Takes the file path of the script to execute and optional arguments.	Takes the command (like ls, echo, etc.) and arguments for the process.
Return Value	Returns a ChildProcess object with IPC communication channels.	Returns a ChildProcess object with streams for input/output.
Use Case	Ideal for creating a new NodeJS process to run JavaScript code in parallel.	Used to run external system commands or shell scripts.

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