100+ Node JS Developer Interview Questions and Answers

Node.js is a runtime environment that allows you to run JavaScript code outside of a web browser.

• Node.js is built on the V8 JavaScript engine from Google Chrome.

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

• Node.js is commonly used for building server-side applications, APIs, and real-time web applications.

• It has a large ecosystem of open-source libraries and frameworks, such as Express.js and Socket.io.

Extract even numbers from an array and store them in a new array using JavaScript.

• Use the filter() method to create a new array with even numbers. Example: [1, 2, 3, 4].filter(num => num % 2 === 0) returns [2, 4].

• The filter() method iterates through each element and applies a condition. If the condition is true, the element is included in the new array.

• You can also use a for loop to achieve the same result. Initialize an empty array and push even numbers into it.

• Example using...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.

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

This program converts an array of strings into an object with indices as keys and values from the array.

• Use a loop to iterate through the array.

• For each element, assign the index as the key and the element as the value in a new object.

• Example: For arr = ['a', 'b', 'c'], the result will be {0: 'a', 1: 'b', 2: 'c'}.

JavaScript is a programming language, while Node.js is a runtime environment for executing JavaScript on the server side.

• JavaScript is primarily used for client-side scripting in web browsers.

• Node.js allows JavaScript to be run on the server, enabling backend development.

• JavaScript runs in the browser's JavaScript engine (like V8 in Chrome).

• Node.js uses the V8 engine to execute JavaScript code outside the browser.

• JavaScript is event-driven and supports asynchronous programmin...read more

Create a form schema with submit and cancel buttons for database interaction.

• Define the form fields: e.g., name, email, age.

• Use a library like Mongoose for MongoDB to create a schema.

• Implement a POST route to handle form submission.

• Add a cancel button that redirects to a previous page or clears the form.

• Ensure validation for form inputs before submission.

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

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

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

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

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.

Designing a high throughput, fault-tolerant system involves scalability, redundancy, and efficient resource management.

• Use microservices architecture to isolate services and improve scalability.

• Implement load balancing to distribute traffic evenly across servers.

• Utilize message queues (e.g., RabbitMQ, Kafka) for asynchronous processing.

• Incorporate database replication and sharding for data availability and performance.

• Design for failure by using health checks and automatic fa...read more

I chose Node.js for its performance, scalability, and the ability to use JavaScript across the stack.

• Asynchronous and event-driven architecture allows handling multiple requests efficiently.

• Single language (JavaScript) for both frontend and backend simplifies development and reduces context switching.

• Rich ecosystem with npm provides access to a vast number of libraries and tools, speeding up development.

• Great for building real-time applications like chat apps or collaborative...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

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

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

This code prints all Saturdays and Sundays for the month of a given date input.

• Use JavaScript's Date object to manipulate dates.

• Extract the month and year from the input date.

• Iterate through the days of the month to find Saturdays (6) and Sundays (0).

• Push the found dates into an array and print them.

• Example input: '2023-10-15' will yield Saturdays and Sundays of October 2023.

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.

This program counts the occurrences of each character in a given string and returns the result as an object.

• Use a loop to iterate through each character in the string.

• Utilize an object to store character counts, initializing counts to zero.

• For each character, increment its count in the object.

• Example: For 'aaabacbdac', the counts would be: {'a': 5, 'b': 2, 'c': 2, 'd': 1}.

setTimeout() can lead to issues like callback hell, unexpected behavior, and timing inaccuracies in JavaScript.

• setTimeout() executes code after a specified delay, but it doesn't guarantee exact timing.

• Nested setTimeout() calls can lead to callback hell, making code hard to read and maintain.

• Using setTimeout() in loops can cause unexpected behavior due to closure capturing the loop variable.

• Example: for (let i = 0; i < 3; i++) { setTimeout(() => console.log(i), 1000); } // Out...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.

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