Glossary

What Is React?

React JavaScript Library

React is a JavaScript library for building user interfaces, created by Meta (Facebook). It uses a component-based architecture where UIs are composed of reusable pieces, each managing its own state. React is the most popular frontend framework, powering Facebook, Instagram, Airbnb, and Netflix.

How React Works

React's key innovation is the component model: build small, reusable UI pieces that compose into complex interfaces. Components accept props (inputs), manage state (internal data), and return JSX (HTML-like syntax in JavaScript).

React 18+ introduced Server Components, which run on the server and send rendered HTML to the client — combining the benefits of server rendering with React's component model. The React ecosystem includes Next.js (full-stack framework), React Router (navigation), and Zustand/Redux (state management).

React's virtual DOM compares the desired UI with the current UI and only updates what changed, making updates efficient. Hooks (useState, useEffect, useContext) replaced class components as the standard way to manage state and side effects.

Why Developers Use React

React dominates frontend development. It's the most in-demand frontend skill, has the largest ecosystem, and is used by most tech companies. Whether you're building a startup MVP or a large enterprise app, React is a safe, productive choice.

Key Concepts

  • Components — Reusable UI building blocks that accept props and manage their own state
  • JSX — HTML-like syntax in JavaScript — <Button onClick={handleClick}>Click me</Button>
  • Hooks — Functions (useState, useEffect) for adding state and side effects to functional components
  • Virtual DOM — React's diffing algorithm that minimizes expensive real DOM updates
  • Server Components — Components that render on the server, reducing client-side JavaScript and improving performance
  • State Management — Managing data flow — useState for local state, Context API for shared state, Zustand/Redux for complex state

React Component with Hooks

jsx
import { useState, useEffect } from 'react';

function UserList() {
  const [users, setUsers] = useState([]);
  const [loading, setLoading] = useState(true);

  useEffect(() => {
    fetch('/api/users')
      .then(res => res.json())
      .then(data => { setUsers(data); setLoading(false); });
  }, []);

  if (loading) return <p>Loading...</p>;

  return (
    <ul>
      {users.map(user => (
        <li key={user.id}>{user.name}</li>
      ))}
    </ul>
  );
}

Learn React — Top Videos

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Frequently Asked Questions

Is React a framework or a library?

Technically a library — it handles the view layer only. Next.js is a React framework that adds routing, SSR, and API routes. In practice, most people use React with additional libraries that together form a framework.

React vs Vue vs Angular — which should I learn?

React has the largest ecosystem and most jobs. Vue is simpler and more beginner-friendly. Angular is full-featured for enterprise apps. For maximum career flexibility, learn React.

Is React hard to learn?

The basics (components, props, state) are straightforward. Hooks, effects, and the broader ecosystem take more time. If you know JavaScript well, you can build simple React apps in a weekend.

Want a structured learning path?

Plan a React Lesson →

Related Terms

Next.jsVueAngularJavaScriptTypeScript

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