100+ 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.

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

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.

Collection framework is a unified architecture for representing and manipulating collections of objects in Java.

• It provides interfaces (such as List, Set, Queue) and classes (such as ArrayList, HashSet, PriorityQueue) to store and manipulate collections of objects.

• It allows for easy insertion, deletion, and retrieval of elements from collections.

• It provides algorithms for searching, sorting, and manipulating collections.

• It promotes code reuse and modularity by providing a com...read more

Error first callback function is a convention in Node.js where the first parameter of a callback function is reserved for an error object.

• The error object is passed as the first argument to the callback function

• If there is no error, the error object will be null or undefined

• If there is an error, the error object will contain information about the error

• This convention allows for consistent error handling in asynchronous operations

• Example: fs.readFile(path, 'utf8', function(err...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

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

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

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

Encapsulation is the process of hiding internal implementation details and exposing only necessary information to the outside world.

• Encapsulation helps in achieving data abstraction and data hiding.

• It allows for better control over the data by preventing direct access to it.

• Encapsulation promotes code reusability and maintainability.

• In Node.js, encapsulation can be achieved using modules and closures.

NoSQL databases are non-relational databases that do not require a fixed schema, while SQL databases are relational databases that use structured query language.

• NoSQL databases are schema-less, allowing for flexible data models.

• SQL databases use a fixed schema with tables and rows.

• NoSQL databases are horizontally scalable, making them suitable for big data applications.

• SQL databases are vertically scalable, meaning they can only handle increased load by increasing the power o...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

NodeJs is a JavaScript runtime built on Chrome's V8 JavaScript engine. ServerSide is a term used to describe code that runs on the server side. Redux is a predictable state container for JavaScript apps. Flex is a CSS layout model. Mongo is a NoSQL database. Express is a web application framework for Node.js.

• NodeJs is a runtime environment that allows you to run JavaScript on the server side.

• ServerSide refers to code that is executed on the server rather than the client side....read more

NodeJS is a server-side JavaScript runtime built on Chrome's V8 JavaScript engine.

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

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

• NodeJS has a large and active community with a vast number of open-source modules available.

• It is commonly used for building web applications, APIs, real-time chat applications, and more.

• NodeJS can be easily integrated with other tec...read more

I implemented Docker and Kubernetes to containerize and orchestrate my NodeJS applications.

• I used Docker to create containers for my NodeJS applications, ensuring consistency and portability.

• I wrote Dockerfiles to define the environment and dependencies for each application.

• I used Docker Compose to define and manage multi-container applications.

• I used Kubernetes to orchestrate and manage the deployment, scaling, and monitoring of my NodeJS applications.

• I created Kubernetes de...read more

Node.js is a runtime environment for executing JavaScript code outside of a web browser.

• Node.js is built on the V8 JavaScript engine, while JavaScript is a programming language.

• Node.js allows JavaScript to be run on the server-side, while JavaScript is primarily used for client-side scripting.

• Node.js provides additional features and APIs for server-side development, such as file system access and networking capabilities.

• JavaScript is used for web development, creating interac...read more

Public, private, and protected are access modifiers used in object-oriented programming to control the visibility of class members.

• Public: accessible from outside the class

• Private: only accessible within the class

• Protected: accessible within the class and its subclasses

Node.js is single-threaded, but can handle multiple threads using child processes or worker threads.

• Use child processes to run multiple instances of Node.js

• Use worker threads for CPU-intensive tasks

• Leverage the cluster module to create a pool of worker processes

Other methods of sorting include bubble sort, selection sort, and insertion sort.

• Bubble sort: repeatedly steps through the list, compares adjacent elements, and swaps them if they are in the wrong order.

• Selection sort: repeatedly finds the minimum element from the unsorted part of the array and swaps it with the first unsorted element.

• Insertion sort: builds the final sorted array one item at a time by inserting each element into its correct position.

Asynchronous nature in Node JS refers to the ability of the program to execute multiple tasks simultaneously without blocking the main thread.

• Allows non-blocking I/O operations, improving performance and scalability

• Uses event-driven architecture to handle multiple requests concurrently

• Uses callbacks, promises, and async/await for handling asynchronous operations

Swagger is a tool for designing, building, and documenting APIs. Adding authentication in Swagger involves using security definitions and security requirements.

• Swagger is a tool used for designing, building, and documenting APIs

• To add authentication in Swagger, you can use security definitions to define authentication methods like API keys, OAuth, etc.

• You can then specify security requirements in your Swagger documentation to enforce authentication for specific endpoints

• For e...read more

NodeJs achieves multiple threading through event loop and asynchronous non-blocking I/O operations.

• NodeJs uses event loop to handle multiple requests efficiently without blocking the main thread.

• It utilizes asynchronous non-blocking I/O operations to perform tasks concurrently.

• NodeJs can also create child processes to handle heavy computational tasks in parallel.

I am currently earning X amount and looking for a competitive salary based on my experience and skills.

• My current CTC is X amount per annum

• I am looking for a competitive salary based on market standards and my experience

• I am open to negotiation based on the job role and responsibilities

Functional components are stateless and use functional syntax, while class components have state and lifecycle methods.

• Functional components are simpler and easier to read/write.

• Class components have access to lifecycle methods like componentDidMount.

• Functional components do not have access to state or lifecycle methods.

• Functional components can use hooks like useState and useEffect to manage state and side effects.

• Example: Functional component - const MyComponent = () => { r...read more

MySql is a relational database management system while NoSql is a non-relational database management system.

• MySql is table-based and uses structured query language (SQL) for querying data.

• NoSql is document-based, key-value pairs, wide-column, or graph-based and does not require a fixed schema.

• MySql is suitable for complex queries and transactions, while NoSql is better for large amounts of unstructured data and horizontal scalability.

• Examples of MySql include Oracle, SQL Serv...read more

Shadowing is when a variable declared within a certain scope has the same name as a variable in an outer scope.

• Occurs when a variable in an inner scope has the same name as a variable in an outer scope

• The inner variable shadows the outer variable within the inner scope

• Can cause unexpected behavior and bugs if not handled properly

Nodejs is a JavaScript runtime built on Chrome's V8 JavaScript engine.

• Nodejs uses an event-driven, non-blocking I/O model.

• It is designed to build scalable network applications.

• Nodejs uses modules to organize code.

• It has a built-in package manager called npm.

• Nodejs can be used for both server-side and client-side programming.

Node.js is used for its non-blocking, event-driven architecture. It is single-threaded to optimize performance.

• Node.js is popular for its asynchronous, non-blocking I/O model which allows for handling multiple requests efficiently.

• Being single-threaded, Node.js can handle a large number of connections without the overhead of creating a new thread for each request.

• Node.js uses event-driven architecture and callbacks to handle requests, making it highly scalable and performant....read more

Program to check whether two strings are anagrams or not

• Convert both strings to lowercase

• Remove all whitespaces from both strings

• Sort both strings alphabetically

• Compare the sorted strings, if they are equal then they are anagrams

A callback function in NodeJS is a function that is passed as an argument to another function and is executed later.

• Callback functions are commonly used in asynchronous programming in NodeJS.

• They allow us to handle the result of an asynchronous operation once it is completed.

• Callback functions can be defined inline or as separate named functions.

• They are often used with functions like setTimeout, readFile, and database queries.

• Callback functions can accept parameters to pass ...read more

OAuth is an open standard for authorization that allows users to grant access to their data without sharing their credentials.

• OAuth is used to authenticate and authorize users in applications.

• It allows users to grant limited access to their data to third-party applications.

• OAuth uses tokens to grant access instead of sharing credentials.

• The OAuth flow involves the client, server, and the authorization server.

• Popular OAuth providers include Google, Facebook, and Twitter.

Design a database schema for a payment gateway interface, cart functionality, and Amazon delivery service.

• Create tables for users, products, orders, payments, and deliveries

• Establish relationships between tables using foreign keys

• Include fields for tracking order status, payment details, and delivery information

• Implement security measures to protect sensitive payment data

• Consider scalability and performance optimization in database design

I deploy my application using containerization and continuous integration/continuous deployment (CI/CD) pipelines.

• Utilize Docker to containerize the application for easy deployment and scalability

• Use CI/CD pipelines such as Jenkins or GitLab CI to automate the deployment process

• Deploy to cloud platforms like AWS, Azure, or Google Cloud for reliable hosting

• Implement monitoring and logging tools like Prometheus and ELK stack for performance tracking

apply, call, and bind are methods used to manipulate the context of a function in JavaScript.

• apply() - calls a function with a given 'this' value and arguments provided as an array

• call() - calls a function with a given 'this' value and arguments provided individually

• bind() - creates a new function that, when called, has its 'this' keyword set to the provided value

Possible reasons for data not reaching backend include network issues, incorrect API endpoints, server errors, and client-side validation errors.

• Network connectivity issues

• Incorrect API endpoints

• Server errors

• Client-side validation errors

EventLoop is a mechanism in Node.js that allows non-blocking I/O operations to be performed asynchronously.

• EventLoop is responsible for handling all I/O operations in Node.js

• It continuously checks the event queue for any new events to be processed

• It executes callbacks when an event is triggered

• It allows Node.js to handle multiple requests simultaneously

• It prevents blocking of the main thread

Promises and callback functions are used in Node.js for handling asynchronous operations.

• Callback functions are functions passed as arguments to another function to be executed later.

• Promises are objects representing the eventual completion or failure of an asynchronous operation.

• Example of callback function: fs.readFile('file.txt', (err, data) => { if (err) throw err; console.log(data); });

• Example of promise: const readFile = new Promise((resolve, reject) => { fs.readFile('f...read more

Fork creates a new process while spawn launches a new process asynchronously.

• Fork is used to create child processes in Node.js, typically for running separate instances of the same application.

• Spawn is used to launch a new process asynchronously, allowing for communication between the parent and child processes.

• Fork is commonly used in cluster mode for load balancing in Node.js applications.

• Spawn is used for executing external commands or scripts in Node.js.

Caching can be implemented using RabbitMQ by storing frequently accessed data in memory.

• Set up a RabbitMQ server to act as a message broker

• Publish data to RabbitMQ when it is fetched from the database

• Subscribe to messages in your Node.js application and store the data in memory

• Check the cache before fetching data from the database

Async await in Node.js is a feature that allows you to write asynchronous code in a synchronous manner.

• Async await is built on top of Promises in Node.js.

• It allows you to write asynchronous code that looks like synchronous code, making it easier to read and maintain.

• The 'async' keyword is used to define a function as asynchronous, while the 'await' keyword is used to wait for a Promise to resolve before continuing.

• Using async await can help avoid callback hell and make error ...read more