Interview Questions and Answers

REST (Representational State Transfer) is an architectural style for designing networked applications. RESTful APIs use standard HTTP methods (GET, POST, PUT, DELETE) for communication.

The Same-Origin Policy restricts web pages from making AJAX requests to a different domain than the one that served the web page, for security reasons.

The virtual DOM is an in-memory representation of the real DOM elements in a React application. It allows React to efficiently update and render components.

CORS (Cross-Origin Resource Sharing) is a security feature that controls how web pages in one domain can request and interact with resources from another domain.

Webpack is a module bundler that transforms and bundles assets, such as JavaScript, CSS, and images, for efficient loading in web applications.

Token-based authentication involves issuing a token (usually a JSON Web Token or JWT) to authenticated users, which is then included in subsequent requests for authorization.

MVC (Model-View-Controller) is a design pattern that separates an application into three interconnected components: Model (data and business logic), View (user interface), and Controller (handles user input and updates the model).

GraphQL is a query language for APIs that allows clients to request only the data they need. It differs from REST by providing more flexibility and reducing over-fetching or under-fetching of data.

Docker is a containerization platform that allows developers to package applications and their dependencies into containers, ensuring consistency across different environments.

WebSockets provide a full-duplex communication channel over a single, long-lived connection, enabling real-time communication between clients and servers.

State management involves managing and updating the state (data) of a web application, ensuring that changes are reflected in the user interface.

SPAs load a single HTML page and dynamically update the content as the user interacts with the application, providing a smoother and more responsive user experience.

JWT is a compact, URL-safe means of representing claims to be transferred between two parties. It is commonly used for authentication by securely transmitting information between parties.

Dependency injection involves providing a component with its dependencies rather than allowing it to create them. It enhances modularity and testability in code.

NoSQL databases provide flexibility, scalability, and better performance for certain types of applications by allowing the storage of unstructured or semi-structured data.

A reverse proxy handles client requests and forwards them to the appropriate backend server, improving security, load balancing, and performance.

Serverless architecture allows developers to build and run applications without managing servers. Advantages include cost efficiency, automatic scaling, and reduced operational overhead.

A load balancer distributes incoming network traffic across multiple servers to ensure no single server is overwhelmed, improving performance and reliability.

Middleware functions in Express.js handle tasks such as authentication, logging, and error handling. They are executed in the request-response cycle before the final request handler.

A web server handles HTTP requests, serving static content, while an application server executes application code, handling dynamic content and business logic.

PWAs are web applications that provide a native app-like experience, including offline functionality, push notifications, and fast loading times. Benefits include improved user engagement and performance.

CSRF is an attack where an attacker tricks a user's browser into making an unintended request. Prevention methods include using anti-CSRF tokens and checking the referer header.

2FA adds an extra layer of security by requiring users to provide two different authentication factors (e.g., password and a temporary code sent to their phone) before accessing an account.

CDNs use caching to store copies of content in multiple locations, reducing server load and improving content delivery speed by serving cached content from the nearest server.

OAuth is an open standard for access delegation, allowing users to grant third-party applications limited access to their resources without sharing their credentials.

A proxy server acts as an intermediary between client requests and the destination server, providing functionalities such as security, load balancing, and content filtering.

'this.props.children' in React.js allows components to pass children elements to other components, enabling the composition of complex UI structures.

A/B testing involves comparing two versions of a web page to determine which performs better. It helps optimize user experiences by analyzing user behavior and preferences.

The 'aria-' attributes in HTML are used for accessibility, providing additional information to assistive technologies. They help convey roles, states, and properties to users with disabilities.

JWT expiration ensures tokens have a limited validity period. Refresh tokens are used to obtain a new JWT without requiring the user to re-enter their credentials, enhancing security.

Server-side caching involves storing copies of dynamically generated content on the server to reduce the need for repeated processing. It improves performance by delivering cached content instead of regenerating it for each request.

GraphQL subscriptions enable real-time data updates by establishing a persistent connection between the client and server. They differ from queries and mutations, which are used for fetching and modifying data, respectively.