Node.js is one of the most popular runtime environments in the world, known for its efficiency, scalability, and ability to handle asynchronous operations. It is built on Chrome’s V8 JavaScript engine for executing JavaScript code outside of a browser. It is extensively used by top companies such as LinkedIn, Netflix, Walmart, Uber, PayPal, NASA, and many more because of its robust features and performance.
In this guide, we will provide 50+ Node.js Interview Questions and Answers tailored for freshers and experienced professionals with 3, 5, and 8 years of experience. Here, we cover everything, including core Node.js concepts, asynchronous programming, event-driven architecture, error handling, design patterns, Node.js modules, and more, that will surely help you to crack Node.js interviews.
Preparing for Node.js interviews requires a deep understanding of core concepts. The Full Stack Development with Node JS course helps you build the practical experience and theoretical knowledge needed to ace full-stack development interviews.
Note: Before proceeding to check these NodeJS interview questions and answers you can learn Node.js with NodeJS Tutorial. This tutorial teaches all important Node.js concepts like modules, file systems, NPM, databases, etc which are often asked in Node Interviews.
Now, let’s discuss interview questions on Node.js. These questions will be helpful in clearing the interviews for the backend developer or full stack developer role.
Node.js Interview Questions and Answers for Freshers
In this section, we discussed basic node.js questions asked in the interview.
Node.js is a JavaScript engine used for executing JavaScript code outside the browser. It is normally used to build the backend of the application and is highly scalable.
JavaScript is a scripting language whereas Node.js is an engine that provides the runtime environment to run JavaScript code.
Here we have difference table between Node.js and JavaScript
| Node.js | JavaScript |
|---|
| Server-side runtime environment | Client-side scripting language |
| Allows running JavaScript code on server | Primarily used for web development |
| Built on Chrome’s V8 JavaScript engine | Runs in a web browser’s JavaScript engine |
| Enables building scalable network applications | Executes code within a browser environment |
| Provides access to file system and network resources | Limited to browser APIs and capabilities |
| Supports event-driven, non-blocking I/O operations | Executes in a single-threaded event loop |
| Used for building backend APIs, servers, and applications | Utilized for creating interactive web pages and client-side logic |
3. Is Node.js single-threaded?
Yes, Node.js is single-threaded by default. However, it utilizes event-driven architecture and non-blocking I/O operations to handle multiple concurrent requests efficiently, enabling scalability and high performance in applications.
4. What kind of API function is supported by Node.js?
There are two types of API functions supported by Node.js:
- Synchronous: These API functions are used for blocking code.
- Asynchronous: These API functions are used for non-blocking code.
5. What is the difference between Synchronous and Asynchronous functions?
Here we have difference table between Synchronous and Asynchronous functions
| Feature | Synchronous Functions | Asynchronous Functions |
|---|
| Execution Blocking | Blocks the execution until the task completes. | Does not block the execution; allows other tasks to proceed concurrently. |
| Waiting for Completion | Executes tasks sequentially; each task must complete before the next one starts. | Initiates tasks and proceeds with other operations while waiting for completion. |
| Return Value | Returns the result immediately after completion. | Typically returns a promise, callback, or uses event handling to handle the result upon completion. |
| Error Handling | Errors can be easily caught with try-catch blocks. | Error handling is more complex and often involves callbacks, promises, or async/await syntax. |
| Usage Scenario | Suitable for simple, sequential tasks with predictable execution flow. | Ideal for I/O-bound operations, network requests, and tasks requiring parallel processing. |
6. What is a module in Node.js?
In Node.js Application, a Module can be considered as a block of code that provide a simple or complex functionality that can communicate with external application. Modules can be organized in a single file or a collection of multiple files/folders. Modules are useful because of their reusability and ability to reduce the complexity of code into smaller pieces. Some examples of modules are. http, fs, os, path, etc.
7. What is npm and its advantages?
npm (Node Package Manager) is the default package manager for Node.js. It allows developers to discover, share, and reuse code packages easily. Its advantages include dependency management, version control, centralized repository, and seamless integration with Node.js projects.
8. What is middleware?
Middleware is the function that works between the request and the response cycle. Middleware gets executed after the server receives the request and before the controller sends the response.
9. How does Node.js handle concurrency even after being single-threaded?
Node.js handles concurrency by using asynchronous, non-blocking operations. Instead of waiting for one task to complete before starting the next, it can initiate multiple tasks and continue processing while waiting for them to finish, all within a single thread.
10. What is control flow in Node.js?
Control flow in Node.js refers to the sequence in which statements and functions are executed. It manages the order of execution, handling asynchronous operations, callbacks, and error handling to ensure smooth program flow.
11. What do you mean by event loop in Node.js?
The event loop in Node.js is a mechanism that allows it to handle multiple asynchronous tasks concurrently within a single thread. It continuously listens for events and executes associated callback functions.
12. What is the order in which control flow statements get executed?
The order in which the statements are executed is as follows:
- Execution and queue handling
- Collection of data and storing it
- Handling concurrency
- Executing the next lines of code
13. What are the main disadvantages of Node.js?
Here are some main disadvantages of Node.js listed below:
- Single-threaded nature: May not fully utilize multi-core CPUs, limiting performance.
- NoSQL preference: Relational databases like MySQL aren’t commonly used.
- Rapid API changes: Frequent updates can introduce instability and compatibility issues.
14. What is REPL in Node.js?
REPL in Node.js stands for Read, Evaluate, Print, and Loop. It is a computer environment similar to the shell which is useful for writing and debugging code as it executes the code in on go.
We use the require module to import the External libraries in Node.js. The result returned by require() is stored in a variable which is used to invoke the functions using the dot notation.
16. What is the difference between Node.js and AJAX?
Node.js is a JavaScript runtime environment that runs on the server side whereas AJAX is a client-side programming language that runs on the browser.
17. What is package.json in Node.js?
package.json in Node.js is a metadata file that contains project-specific information such as dependencies, scripts, version, author details, and other configuration settings required for managing and building the project.
JavaScript
const http = require('http');
// Create a server object
http.createServer(function (req, res) {
res.write('Hello World!');
res.end();
}).listen(3000);
Run this program from the command line and see the output in the browser window. This program prints Hello World on the browser when the browser sends a request through http://localhost:3000/.
19. What is the most popular Node.js framework used these days?
The most famous Node.js framework used is Express.js as it is highly scalable, efficient, and requires very few lines of code to create an application.
A promise is basically an advancement of callbacks in NodeJS. In other words, a promise is a JavaScript object which is used to handle all the asynchronous data operations. While developing an application you may encounter that you are using a lot of nested callback functions which causes a problem of callback hell. Promises solve this problem of callback hell.
Node.js Interview Questions & Answers
In this set we will be looking at intermediate Node Interview Question for candidates with over 2 years of experience.
21. What is event-driven programming in Node.js?
Event-driven programming is used to synchronize the occurrence of multiple events and to make the program as simple as possible. The basic components of an Event-Driven Program are:
- A callback function ( called an event handler) is called when an event is triggered.
- An event loop that listens for event triggers and calls the corresponding event handler for that event.
22. What is buffer in Node.js?
The Buffer class in Node.js is used to perform operations on raw binary data. Generally, Buffer refers to the particular memory location in memory. Buffer and array have some similarities, but the difference is array can be any type, and it can be resizable. Buffers only deal with binary data, and it can not be resizable. Each integer in a buffer represents a byte. console.log() function is used to print the Buffer instance.
Streams are a type of data-handling method and are used to read or write input into output sequentially. Streams are used to handle reading/writing files or exchanging information in an efficient way. The stream module provides an API for implementing the stream interface. Examples of the stream object in Node.js can be a request to an HTTP server and process.stdout are both stream instances.
The crypto module is used for encrypting, decrypting, or hashing any type of data. This encryption and decryption basically help to secure and add a layer of authentication to the data. The main use case of the crypto module is to convert the plain readable text to an encrypted format and decrypt it when required.
25. What is callback hell?
Callback hell is an issue caused due to a nested callback. This causes the code to look like a pyramid and makes it unable to read To overcome this situation we use promises.
The Timers module in Node.js contains various functions that allow us to execute a block of code or a function after a set period of time. The Timers module is global, we do not need to use require() to import it.
It has the following methods:
The process.nextTick() method is used to add a new callback function at the start of the next event queue. it is called before the event is processed. The setImmediate is called at the check phase of the next event queue. It is created in the poll phase and is invoked during the check phase.
The setImmediate function is used to execute a particular script immediately whereas the setTimeout function is used to hold a function and execute it after a specified period of time.
Both these methods are used to create new child processes the only difference between them is that spawn() method creates a new function that Node runs from the command line whereas fork() function creates an instance of the existing fork() method and creates multiple workers to perform on the same task.
The passport module is used for adding authentication features to our website or web app. It implements authentication measure which helps to perform sign-in operations.
31. What is fork in Node.js?
Fork is a method in Node.js that is used to create child processes. It helps to handle the increasing workload. It creates a new instance of the engine which enables multiple processes to run the code.
The three methods to avoid callback hell are:
- Using async/await()
- Using promises
- Using generators
Body-parser is the Node.js body-parsing middleware. It is responsible for parsing the incoming request bodies in a middleware before you handle it. It is an NPM module that processes data sent in HTTP requests.
The word CORS stands for “Cross-Origin Resource Sharing”. Cross-Origin Resource Sharing is an HTTP-header based mechanism implemented by the browser which allows a server or an API to indicate any origins (different in terms of protocol, hostname, or port) other than its origin from which the unknown origin gets permission to access and load resources. The cors package available in the npm registry is used to tackle CORS errors in a Node.js application.
35. Explain the tls module in Node.js?
The tls module provides an implementation of the Transport Layer Security (TLS) and Secure Socket Layer (SSL) protocols that are built on top of OpenSSL. It helps to establish a secure connection on the network.
For further reading, check out our dedicated article on Intermediate Node Interview Questions and Answers. Inside, you’ll discover 20+ questions with detailed answers.
Advanced Node.js Interview Questions for Experienced
In this set we will be covering Node interview question for experienced developers with over 5 years of experience.
Due to a single thread in node.js, 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.
- 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 child process which is global.
- send(): It sends a message from worker to master or vice versa.
- kill(): It is used to kill the current worker.
Session management can be done in node.js 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.
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.
40. How can we implement authentication and authorization in Node.js?
Authentication is the process of verifying a user’s identity while authorization is determining what actions can be performed. We use packages like Passport and JWT to implement authentication and authorization.
The package used for file uploading in Node.js 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 node.js middleware that is used for handling multipart/form-data, which is a mostly used library for uploading files.
Node.js is the best choice for asynchronous programming Python is not the best choice for asynchronous programming. Node.js is best suited for small projects to enable functionality that needs less amount of scripting. Python is the best choice if you’re developing larger projects. Node.js is best suited for memory-intensive activities. Not recommended for memory-intensive activities. Node.js is a better option if your focus is exactly on web applications and website development. But, Python is an all-rounder and can perform multiple tasks like- web applications, integration with back-end applications, numerical computations, machine learning, and network programming. Node.js is an ideal and vibrant platform available right now to deal with real-time web applications. Python isn’t an ideal platform to deal with real-time web applications. The fastest speed and great performance are largely due to Node.js being based on Chrome’s V8 which is a very fast and powerful engine. Python is slower than Node.js, As Node.js is based on fast and powerful Chrome’s V8 engine, Node.js utilizes JavaScript interpreter. Python using PyPy as Interpreter. In case of error handling and debugging Python beats Node.js. Error handling in Python takes significantly very little time and debugging in Python is also very easy compared to Node.js.
43. How to handle database connection in Node.js?
To handle database connection in Node.js 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.
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
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 Node.js developers as it reduces the cache size which makes the application more efficient. However, it is very easy to integrate Redis with Node.js applications.
Web Socket is a protocol that provides full-duplex (multiway) communication i.e. allows communication in both directions simultaneously. It 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. Traditionally on the web, we had a request/response format where a user sends an HTTP request and the server responds to that. This is still applicable in most cases, especially those using RESTful API. But a need was felt for the server to also communicate with the client, without getting polled(or requested) by the client. The server in itself should be able to send information to the client or the browser. This is where Web Socket comes into the picture.
The Util module in node.js provides access to various utility functions. There are various utility modules available in the node.js module library.
- OS Module: Operating System-based utility modules for node.js are provided by the OS module.
- Path Module: The path module in node.js 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 node.js is used for the creation of both client and server. Similar to DNS Module this module also provides an asynchronous network wrapper.
We use process.env to handle environment variables in Node.js. 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
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.
50. What are child processes in Node.js?
Usually, Node.js 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.
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.
For further reading, check out our dedicated article on Advanced Node Interview Questions. Inside, you’ll discover 20+ questions with detailed answers.
Conclusion
This Node interview questions and answers gives you an overview of what type of questions can be asked on Node.js in your interview. Node.js is very important JavaScript framework that is asked in job interviews for Node.js Developer, Full-Stack Node.js Developer, DevOps Engineer with Node.js, etc. Many big companies like Netflix, PayPal,Meta, Uber, etc hire for Node.js expert.
Practicing before interviews gives you upperhand over other candidates. Hope this helps you crack your dream job interview!!