200+ Node JS Developer Interview Questions and Answers

The main modules of Node.js are HTTP, File System, Path, and Events.

• HTTP module allows Node.js to transfer data over the HyperText Transfer Protocol (HTTP).

• File System module enables interaction with the file system, allowing reading, writing, and manipulating files.

• Path module provides utilities for working with file and directory paths.

• Events module allows for event-driven programming, enabling the creation and handling of custom events.

Questions related to backend development concepts and technologies.

• Joins in MySQL are used to combine data from two or more tables based on a related column.

• Middleware is software that acts as a bridge between different applications or systems.

• JWT (JSON Web Token) is a standard for securely transmitting information between parties as a JSON object.

• POST is used to submit data to be processed, PUT is used to update existing data, and GET is used to retrieve data.

• RDBMS (Relation...read more

Node.js is a JavaScript runtime built on Chrome's V8 JavaScript engine, used for server-side and networking applications.

• Node.js is an open-source, cross-platform runtime environment for executing JavaScript code outside of a browser.

• It uses an event-driven, non-blocking I/O model that makes it lightweight and efficient.

• Node.js allows developers to build scalable and high-performance applications.

• It provides a rich set of built-in modules and libraries for various functionali...read more

Nodejs application can be deployed using various tools like Heroku, AWS, DigitalOcean, etc.

• Use a cloud platform like Heroku, AWS, DigitalOcean, etc.

• Create a production build of the application

• Configure environment variables

• Use a process manager like PM2 to manage the application

• Use a reverse proxy like Nginx to handle incoming requests

• Set up SSL/TLS certificates for secure communication

Yes, I follow agile methodology for software development.

• I believe in iterative development and continuous feedback.

• I prioritize customer satisfaction and collaboration with the team.

• I use tools like Jira and Trello to manage tasks and sprints.

• I also follow the Scrum framework for daily stand-ups, sprint planning, and retrospectives.

Streams are objects that allow reading or writing data continuously. There are four types of streams: Readable, Writable, Duplex, and Transform.

• Streams are used to handle large amounts of data efficiently.

• They can be used for reading data from a source or writing data to a destination.

• Streams can be piped together to create a data flow.

• Example: Reading a file using a Readable stream and writing it to another file using a Writable stream.

Cluster is a group of processes that share the same resources while thread is a lightweight process that shares the same memory.

• Cluster is used for scaling and load balancing while thread is used for improving performance.

• Cluster can run on multiple machines while thread runs within a single process.

• Cluster requires inter-process communication while thread does not.

• Examples of cluster include PM2 and Node.js cluster module while examples of thread include worker threads in No...read more

Use Node.js streams to efficiently process large CSV data.

• Use the 'fs' module to create a read stream for the CSV file.

• Use a CSV parsing library like 'csv-parser' to parse the data row by row.

• Process each row asynchronously to avoid blocking the event loop.

• Use a database like MongoDB or PostgreSQL to store the processed data if needed.

var, let, and const are used to declare variables in JavaScript with different scoping and mutability.

• var has function scope and can be redeclared and reassigned

• let has block scope and can be reassigned but not redeclared

• const has block scope and cannot be reassigned or redeclared

The setTimeout function in JavaScript is used to schedule a task to be executed after a specified delay.

• The setTimeout function takes two parameters: a callback function and a delay time in milliseconds.

• The callback function is executed after the specified delay.

• The setTimeout function returns a unique identifier (timer ID) that can be used to cancel the execution of the callback function using the clearTimeout function.

• The output of the setTimeout function itself is not sign...read more

The code demonstrates the behavior of 'this' keyword with arrow functions and normal functions.

• Arrow functions do not bind their own 'this' value, it inherits 'this' from the surrounding scope.

• Normal functions have their own 'this' value, which is determined by how the function is called.

• Arrow functions are useful when you want to preserve the value of 'this' from the surrounding context.

This code takes user input, calculates the sum, and prints the result using JavaScript.

• Use prompt() to take user input in a browser environment.

• Convert input strings to numbers using parseInt() or parseFloat().

• Use a loop to allow multiple inputs until a specific condition is met.

• Example: let sum = 0; while (true) { let input = prompt('Enter a number (or type exit):'); if (input === 'exit') break; sum += parseFloat(input); } console.log('Total Sum:', sum);

For designing Swiggy, I would choose a tech stack that ensures scalability, performance, and real-time data processing.

• Node.js: Ideal for handling multiple requests simultaneously, making it suitable for a food delivery platform with high traffic.

• Express.js: A minimal and flexible Node.js web application framework that provides a robust set of features for web and mobile applications.

• MongoDB: A NoSQL database that allows for flexible data storage and quick retrieval, essentia...read more

To connect to MongoDB from NodeJS backend, use the 'mongodb' package and the 'MongoClient' class.

• Install the 'mongodb' package using npm: npm install mongodb

• Require the 'mongodb' package in your NodeJS file: const MongoClient = require('mongodb').MongoClient

• Create a connection URL with the appropriate MongoDB server details: const url = 'mongodb://localhost:27017/mydatabase'

• Use the 'MongoClient' class to connect to the MongoDB server: MongoClient.connect(url, function(err, db...read more

I have used Redis cache in multiple projects to improve performance and reduce database load.

• Used Redis cache to store frequently accessed data for faster retrieval

• Implemented Redis cache in a Node.js application to cache API responses

• Utilized Redis cache to store session data for improved user experience

Node.js uses event-driven architecture to handle asynchronous tasks while synchronous tasks are executed in a blocking manner.

• Node.js uses event loop to handle asynchronous tasks by offloading them to the system, allowing other tasks to continue without waiting.

• Synchronous tasks are executed in a blocking manner, meaning the program waits for each task to complete before moving on to the next one.

• Node.js provides non-blocking I/O operations which allow multiple tasks to be ex...read more

Spread operator allows an iterable to be expanded in places where zero or more arguments or elements are expected. Rest operator collects all the remaining elements into an array.

• Spread operator is denoted by three dots (...) and is used to expand elements of an iterable like an array or object.

• Rest operator is also denoted by three dots (...) and is used to collect multiple elements into a single array.

• Spread operator example: const arr1 = [1, 2, 3]; const arr2 = [...arr1, 4...read more

A meeting booking application requires a schema to manage users, meetings, and availability efficiently.

• Users Table: Stores user information (e.g., user_id, name, email).

• Meetings Table: Contains meeting details (e.g., meeting_id, title, description, start_time, end_time).

• Availability Table: Tracks user availability (e.g., user_id, date, start_time, end_time).

• Participants Table: Links users to meetings (e.g., meeting_id, user_id, status).

• Notifications Table: Manages reminders ...read more

Async await simplifies asynchronous code by allowing it to be written in a synchronous style.

• Async await makes asynchronous code easier to read and write compared to callbacks and promises.

• It allows developers to write asynchronous code in a more synchronous manner, making it easier to understand and maintain.

• Async await also helps in error handling by allowing try-catch blocks to be used with asynchronous code.

• It eliminates the need for chaining multiple .then() methods when...read more

Designing a scalable Node.js app for 100,000 concurrent connections requires efficient architecture and resource management.

• Use a load balancer (e.g., Nginx) to distribute traffic across multiple Node.js instances.

• Implement clustering with Node.js's built-in cluster module to utilize multi-core systems.

• Leverage asynchronous programming to handle I/O operations without blocking the event loop.

• Utilize a message broker (e.g., RabbitMQ, Kafka) for decoupling services and managing...read more

The event loop is a core concept in Node.js that manages asynchronous operations and handles tasks efficiently.

• The event loop allows Node.js to perform non-blocking I/O operations despite being single-threaded.

• I/O-bound tasks (like file reading) are handled asynchronously, allowing other operations to continue.

• CPU-bound tasks (like heavy computations) can block the event loop, causing delays in handling I/O tasks.

• Example of I/O-bound: Reading a file using fs.readFile() allows...read more

SQL command to get the TOP 3 list in a data set

• Use the SELECT statement to retrieve data from the table

• Use the ORDER BY clause to sort the data in descending order

• Use the LIMIT clause to limit the result set to 3 rows

Implementing middleware changes can help mitigate DDoS attacks by controlling traffic and enhancing security measures.

• Rate Limiting: Implement rate limiting to restrict the number of requests a user can make in a given time frame, e.g., 100 requests per minute.

• IP Blacklisting: Maintain a list of known malicious IP addresses and block requests from them to prevent attacks from those sources.

• Request Throttling: Introduce throttling mechanisms to slow down the response for users...read more

I have extensive experience in building task management APIs using Node.js, focusing on scalability and performance.

• Utilized Express.js to create RESTful APIs for task management, allowing CRUD operations for tasks.

• Implemented JWT authentication for secure access to the API endpoints.

• Used MongoDB as the database to store task data, leveraging Mongoose for schema definition and data validation.

• Integrated third-party services like Slack for notifications when tasks are updated ...read more

Explaining loop logic in JavaScript without using built-in methods.

• Use 'for' loops to iterate through arrays: for (let i = 0; i < arr.length; i++) { console.log(arr[i]); }

• Implement 'while' loops for conditional iteration: let i = 0; while (i < arr.length) { console.log(arr[i]); i++; }

• Utilize 'do...while' loops for at least one execution: let i = 0; do { console.log(arr[i]); i++; } while (i < arr.length);

• Nested loops can be used for multi-dimensional arrays: for (let i = 0; i ...read more

A web developer is responsible for designing, coding, and maintaining websites and web applications.

• Designing and developing websites and web applications using programming languages such as HTML, CSS, and JavaScript

• Collaborating with designers and other team members to ensure the website meets the client's requirements

• Testing and debugging websites to ensure they are functioning correctly across different browsers and devices

• Updating and maintaining websites to keep them cur...read more

Popular Node.js frameworks include Express, Koa, NestJS, and Hapi, each offering unique features for web development.

• Express: Minimalist framework, great for building RESTful APIs quickly.

• Koa: Created by the same team as Express, it uses async/await for better error handling.

• NestJS: A progressive framework for building efficient, reliable, and scalable server-side applications.

• Hapi: Focuses on configuration-driven development, ideal for building robust applications.