60+ Full Stack Web Developer Interview Questions and Answers

Time complexity to add an element to a Singly Linked List is O(1) if added at the end using Tail pointer, and O(n) if added anywhere in the middle.

• Adding an element at the end of a Singly Linked List using the Tail pointer is a constant time operation, hence O(1).

• Adding an element anywhere in the middle of a Singly Linked List requires traversing the list to find the insertion point, resulting in a time complexity of O(n).

• For example, if we have a Singly Linked List with 5 el...read more

Overloading is having multiple methods with the same name but different parameters, while overriding is implementing a method in a subclass that is already defined in the superclass.

• Overloading allows a class to have multiple methods with the same name but different parameters.

• Overriding involves implementing a method in a subclass that is already defined in the superclass.

• Example: Overloading - having multiple constructors in a class with different parameters. Overriding - i...read more

NextJs is a framework built on top of ReactJs, providing server-side rendering and other features for easier development.

• NextJs is a framework built on top of ReactJs, providing server-side rendering, routing, and other features for easier development.

• ReactJs is a JavaScript library for building user interfaces, while NextJs is a framework that adds functionality like server-side rendering and routing to React applications.

• NextJs simplifies the process of building React appli...read more

Optimizing JSON involves minimizing redundant data, using efficient data structures, and compressing data when necessary.

• Minimize redundant data by using references or IDs instead of repeating the same information multiple times.

• Use efficient data structures like arrays or dictionaries to store JSON data in a more organized and accessible way.

• Compress JSON data using techniques like gzip or deflate to reduce file size and improve loading times.

• Example: Instead of storing the ...read more

JavaScript concepts include variables, functions, objects, and more, each with real-life analogies for better understanding.

• Variables: Like containers that hold different items (data types) such as numbers, strings, or objects.

• Functions: Similar to a recipe; you define a set of instructions (code) to perform a specific task when called.

• Objects: Think of an object as a car; it has properties (color, model) and methods (drive, stop) that define its behavior.

• Arrays: Like a list ...read more

Time complexity measures the amount of time an algorithm takes to complete as a function of the input size.

• Time complexity is expressed using Big O notation (e.g., O(n), O(log n)).

• O(1) - Constant time: Example - Accessing an element in an array by index.

• O(n) - Linear time: Example - Finding an element in an unsorted array.

• O(n^2) - Quadratic time: Example - Bubble sort algorithm.

• O(log n) - Logarithmic time: Example - Binary search in a sorted array.

Implement a live data fetching dashboard with efficient memory management using techniques like polling and cleanup.

• Use setInterval to fetch data every 10 seconds: setInterval(fetchData, 10000);

• Implement cleanup logic to clear previous data before fetching new data to avoid memory leaks.

• Utilize WebSockets for real-time data updates if the server supports it, reducing the need for frequent polling.

• Consider using a state management library (like Redux) to manage data efficientl...read more

Data can be sent from frontend to backend using HTTP requests such as POST or GET.

• Use AJAX or fetch API to send data asynchronously

• Include data in the request body or URL parameters

• Backend should have an API endpoint to receive the data

• Use appropriate data format such as JSON or form data

Design a flexible schema for user roles and permissions in an enterprise app to manage access across multiple modules.

• Use a many-to-many relationship between Users, Roles, and Permissions to allow flexibility.

• Create a 'Users' table with user details and a 'Roles' table for different roles like Admin, Editor, Viewer.

• Implement a 'Permissions' table that defines specific actions like 'create', 'read', 'update', 'delete'.

• Link Roles to Permissions through a 'RolePermissions' table...read more

Find the smallest prime number in a given array of numbers.

• A prime number is greater than 1 and has no divisors other than 1 and itself.

• Example: In the array [4, 6, 8, 3, 5], the smallest prime is 3.

• To find the smallest prime, iterate through the array and check each number for primality.

• Use a helper function to determine if a number is prime.

Deploying a full stack app involves setting up the environment, configuring settings, and pushing code to Heroku or Vercel.

• 1. Prepare your app: Ensure your app is production-ready, with necessary configurations for both frontend and backend.

• 2. Create a Heroku/Vercel account: Sign up and log in to your account on the respective platform.

• 3. Install CLI tools: For Heroku, install the Heroku CLI; for Vercel, install the Vercel CLI.

• 4. Initialize your project: For Heroku, run 'hero...read more

HTTP status codes indicate the result of a server's response to a client's request, each serving a specific purpose.

• 301: Moved Permanently - Indicates that a resource has been permanently moved to a new URL. Example: Redirecting from oldsite.com to newsite.com.

• 401: Unauthorized - Indicates that authentication is required and has failed or has not yet been provided. Example: Accessing a protected resource without login.

• 403: Forbidden - Indicates that the server understands the...read more

SQL joins combine rows from two or more tables based on related columns, enabling complex queries and data retrieval.

• INNER JOIN: Returns records with matching values in both tables. Example: SELECT * FROM A INNER JOIN B ON A.id = B.a_id;

• LEFT JOIN (or LEFT OUTER JOIN): Returns all records from the left table and matched records from the right table. Example: SELECT * FROM A LEFT JOIN B ON A.id = B.a_id;

• RIGHT JOIN (or RIGHT OUTER JOIN): Returns all records from the right table ...read more

React's Virtual DOM optimizes rendering by minimizing direct DOM manipulations, enhancing performance during updates.

• The Virtual DOM is a lightweight copy of the actual DOM, allowing React to efficiently determine changes.

• During a re-render, React compares the new Virtual DOM with the previous one using a diffing algorithm.

• Only the components that have changed are updated in the actual DOM, reducing performance costs.

• React uses reconciliation to identify which parts of the UI...read more

Design a secure REST API for managing user roles and permissions with proper authentication and authorization.

• Use OAuth 2.0 for secure token-based authentication.

• Implement role-based access control (RBAC) to restrict access to endpoints.

• Validate user permissions before processing requests, e.g., check if a user has 'admin' role for certain actions.

• Use HTTPS to encrypt data in transit, preventing eavesdropping.

• Rate limit API requests to mitigate brute force attacks.

CORS issues arise when a web application requests resources from a different origin, leading to security restrictions.

• CORS stands for Cross-Origin Resource Sharing, a security feature implemented by browsers.

• When a React app (frontend) tries to access an API (backend) on a different domain, CORS policies may block the request.

• To resolve CORS issues in an Express app, use the 'cors' middleware: `const cors = require('cors'); app.use(cors());`

• You can configure CORS to allow spe...read more

Implementing security measures like input validation and tokenization to protect against XSS and CSRF attacks.

• Use input validation and sanitization to prevent XSS. For example, use libraries like DOMPurify to clean user input.

• Implement Content Security Policy (CSP) to restrict sources of content and mitigate XSS risks.

• Use anti-CSRF tokens in forms and AJAX requests to ensure that requests are legitimate. For example, include a token in the form that is validated on the server...read more

Managing state in large-scale applications can be achieved using Redux, Context API, or other solutions based on specific needs.

• Redux is ideal for complex state management with a predictable state container, making it easier to debug and test.

• Context API is suitable for simpler state management needs, allowing for easier integration without additional libraries.

• For example, Redux can manage global state like user authentication, while Context API can handle theme settings.

• Con...read more

Event delegation is a technique in JavaScript that allows handling events at a higher level in the DOM hierarchy.

• Event delegation works by attaching a single event listener to a parent element instead of multiple listeners to child elements.

• When an event occurs on a child element, it bubbles up to the parent, allowing the parent listener to handle it.

• This reduces memory usage and improves performance, especially with many child elements.

• Example: Instead of adding click listen...read more

SQL joins combine rows from two or more tables based on related columns, with different types defining how unmatched rows are handled.

• INNER JOIN: Returns only matching rows from both tables. Example: SELECT * FROM A INNER JOIN B ON A.id = B.id.

• LEFT JOIN: Returns all rows from the left table and matched rows from the right table. Unmatched rows in the right table will be NULL. Example: SELECT * FROM A LEFT JOIN B ON A.id = B.id.

• RIGHT JOIN: Returns all rows from the right table...read more

API versioning in RESTful backends ensures compatibility and smooth transitions between different API versions.

• Use URI versioning: e.g., /api/v1/resource and /api/v2/resource.

• Implement query parameter versioning: e.g., /api/resource?version=1.

• Utilize header versioning: clients specify the version in request headers.

• Maintain backward compatibility to avoid breaking changes for existing clients.

• Document each version clearly to guide developers on usage and changes.

Create Express.js middleware to authenticate API requests using JWT from the Authorization header.

• Use the 'jsonwebtoken' library to verify the JWT token.

• Extract the token from the 'Authorization' header: 'Bearer <token>'.

• Check if the token is valid and not expired.

• If valid, attach the user information to the request object for further use.

• Send a 401 response if the token is missing or invalid.

Display a list of products from an API in a React component using state and effects.

• Use useState to manage the product list state. Example: const [products, setProducts] = useState([]);

• Use useEffect to fetch data from the API when the component mounts. Example: useEffect(() => { fetchProducts(); }, []);

• Implement a function to fetch products from the API. Example: const fetchProducts = async () => { const response = await fetch(apiUrl); const data = await response.json(); setP...read more

Concurrency in Node.js can be managed using techniques like callbacks, promises, and async/await to ensure data integrity.

• Use asynchronous programming with callbacks to handle multiple requests without blocking the event loop.

• Implement Promises to manage asynchronous operations more effectively, allowing for cleaner code and better error handling.

• Utilize async/await syntax for a more synchronous-like flow, making it easier to read and maintain code.

• Consider using a message qu...read more

Implemented features like real-time notifications, user roles, and advanced search for enhanced user experience.

• Real-time notifications using WebSockets for instant updates on user activities.

• User roles and permissions to manage access levels, ensuring data security.

• Advanced search functionality with filters for improved content discovery.

• Responsive design for seamless experience across devices.

• Integration of third-party APIs for enhanced functionality, like payment gateways.

The frontend and backend can be linked through APIs, where the frontend sends requests to the backend and receives responses.

• Use RESTful APIs to define endpoints and methods for communication between frontend and backend

• Frontend makes HTTP requests to backend APIs using libraries like Axios or Fetch

• Backend processes the requests, performs necessary operations, and sends back responses

• Responses can be in various formats like JSON or XML

• Examples: a frontend form submitting data...read more

Multiple files can be uploaded using AJAX by sending a FormData object containing the files.

• Create a FormData object

• Append each file to the FormData object

• Send the FormData object using AJAX