React Hooks revolutionized how we write React components. They allow you to use state and other React features without writing class components.

## useState Hook

The useState Hook lets you add state to functional components. It returns an array with two elements: the current state value and a function to update it.

## useEffect Hook

The useEffect Hook lets you perform side effects in functional components. It serves the same purpose as componentDidMount, componentDidUpdate, and componentWillUnmount in class components.

## Best Practices

When using Hooks, always follow the Rules of Hooks: only call Hooks at the top level and only call Hooks from React functions.

Master the most commonly used React Hooks: useState and useEffect with practical examples.

React Hooks: A Complete Guide to useState and useEffect

This comprehensive guide covers 50 essential React.js interview questions that every developer should know. These questions cover fundamental concepts, hooks, performance optimization, and advanced patterns commonly asked in technical interviews.

## Core Concepts

Understanding React's core concepts is essential for any React developer. These questions test your knowledge of components, props, state, and the component lifecycle.

## React Hooks

Hooks revolutionized React development by allowing functional components to use state and lifecycle features. Master these questions to demonstrate your understanding of modern React patterns.

## Performance Optimization

React performance is crucial for building fast applications. These questions cover memoization, code splitting, lazy loading, and other optimization techniques.

## Advanced Patterns

Advanced React patterns include context API, error boundaries, render props, higher-order components, and custom hooks. These questions test your ability to solve complex problems.

Comprehensive collection of 50 essential React.js interview questions covering hooks, components, state management, performance, and advanced concepts.

React.js Interview Questions: 50 Essential Questions for Developers

React Server Components are probably the biggest change to React in years. If you're building React apps in 2025, you need to understand this.

## What Are Server Components?

Think of Server Components as components that run on your server, not in the browser. They can directly access your database, read files, and do server stuff. The cool part? They never send JavaScript to the browser, so your pages load faster.

## Server vs Client Components

Here's the simple rule: use Server Components for fetching data and showing static content. Use Client Components (the regular ones you know) for buttons, forms, and anything interactive.

## Using Them in Next.js

Next.js 13+ makes this super easy. By default, every component is a Server Component. Just add 'use client' at the top when you need interactivity. That's it!

## Why This Matters

Your app will be faster, use less JavaScript, and feel more responsive. It's like having the best of both worlds - server-side rendering and client-side interactivity.

React Server Components are changing how we build React apps in 2025. Learn what they are, when to use them, and how they make your apps faster. This is the future of React.

React Server Components: The Game Changer

React 19 is here and it brings some exciting changes. If you're building React apps in 2025, you need to know what's new. Don't worry, I'll explain everything in simple terms.

## What's New in React 19?

React 19 introduces server actions, automatic batching improvements, better error handling with error boundaries, and improved performance. The best part? It's backward compatible, so your existing code will still work.

## Server Actions

Server actions let you call server functions directly from your React components. No more API routes for simple operations. Just write a function and call it - React handles everything.

## Better Error Handling

React 19 makes error boundaries easier to use. Your app won't crash completely when something goes wrong. Plus, better error messages make debugging way easier.

## Performance Improvements

Automatic batching works everywhere now, not just in event handlers. Your app will re-render less often and feel faster. These improvements happen automatically - no code changes needed.

## Getting Started

I'll show you how to upgrade and start using React 19 features. Most of them work automatically, but some require small changes to unlock new capabilities.

Discover React 19's new features and improvements. Learn about actions, automatic batching, better error handling, and how React 19 makes building apps easier and faster.

React 19: What's New and Why It Matters

If you're still using useState and useEffect for fetching data, you're doing it the hard way. React Query makes data fetching simple, fast, and reliable. Your app will feel instant because data is cached and synchronized automatically.

## Why React Query?

React Query handles caching, background updates, error states, loading states, and more - all automatically. You write less code, and your app feels faster because data is cached intelligently.

## Basic Usage

Getting started is super simple. Wrap your app with QueryClientProvider and use the useQuery hook. React Query handles loading, error, and success states automatically. No more manual state management for API calls.

## Mutations

When you need to create, update, or delete data, use useMutation. React Query can automatically refetch related queries after mutations, keeping your UI in sync with your server.

## Advanced Features

Learn about infinite queries for pagination, optimistic updates for instant UI feedback, and query invalidation for cache management. These patterns will make your app feel professional.

Learn React Query (TanStack Query) for better data fetching. Stop using useState and useEffect for API calls. React Query handles caching, loading states, and errors automatically.

React Query: Better Data Fetching

Passing props through many components gets annoying fast. React Context lets you share data with any component without prop drilling. Perfect for themes, user data, or any global state.

## What is Context?

Context provides a way to pass data through the component tree without passing props down manually at every level. Create a context, provide a value, and consume it anywhere in your component tree.

## Creating Context

It's simple - use createContext to create a context, then use Provider to wrap components that need access to it. Any component inside the Provider can access the context value.

## Using Context

Use the useContext hook to access context values. It's cleaner than prop drilling and works great for data that many components need, like user info or theme settings.

## Best Practices

I'll show you when to use Context vs props, how to avoid unnecessary re-renders, and how to structure your context for better performance. These patterns will make your code cleaner.

Master React Context API for sharing state across components. Learn when to use Context vs props, and how to avoid unnecessary re-renders. Perfect for theme, user data, or any global state.

React Context API: Global State Made Simple

CORS errors in React happen when your app tries to call an API from a different origin. Understanding how to handle this is crucial for building React applications.

## What Causes CORS Errors in React?

When your React app (running on localhost:3000) tries to fetch data from an API (running on localhost:5000), the browser blocks it due to CORS policy. This is a browser security feature.

## Solutions for Development

For development, you have several options:
- Use a proxy in package.json
- Use a proxy in vite.config.js (if using Vite)
- Configure the backend to allow your origin

## Solutions for Production

In production, you need to:
- Ensure backend allows your frontend domain
- Use proper CORS configuration
- Handle credentials correctly

## Using Fetch with CORS

Learn how to properly configure fetch requests to work with CORS-enabled APIs. This includes setting headers and credentials.

## Proxy Configuration

Setting up a proxy is the easiest solution for development. It makes your API calls appear to come from the same origin.

## Common Mistakes

I'll show you common mistakes developers make and how to avoid them. These tips will save you hours of debugging.

Learn how to handle and fix CORS errors in React applications. Understand proxy configuration, fetch options, and how to work with APIs. Essential for React developers.

Fixing CORS Errors in React Applications

Master React development with hooks, state management, and modern patterns.

React Tutorials

All React Tutorials