React is a JavaScript library for building user interfaces, created by Meta (formerly Facebook) and maintained as an open-source project. It is the most widely used front-end library in 2026, powering interfaces at companies like PayPal, Netflix, Airbnb, and Shopify.<\/p>\n
What makes React different from earlier approaches is its component-based architecture<\/strong>: you build UIs out of self-contained, reusable pieces (components) that each manage their own logic and rendering. This makes complex interfaces manageable, testable, and scalable.<\/p>\n This guide explains React from the ground up \u2014 what it is, how it works, and why it matters to both developers and<\/em> designers in 2026.<\/p>\n Design with real React components<\/p>\n UXPin Merge lets you drag and drop production React components into your design \u2014 what you design is what developers ship.<\/p>\n<\/p>\n<\/div>\n Try UXPin Merge<\/a>\n<\/div>\n React (also called React.js or ReactJS) is a declarative, component-based JavaScript library<\/strong> for building user interfaces. Unlike full frameworks (Angular, for example), React focuses specifically on the view layer \u2014 how things look and respond to user interaction.<\/p>\n Key characteristics:<\/p>\n React is technically a library<\/strong>, not a framework. A framework (like Angular or Vue) provides opinions and tooling for routing, state management, build processes, and more. React handles only UI rendering; you choose separate libraries for everything else (React Router for routing, Zustand or Redux for state management, etc.).<\/p>\n That said, meta-frameworks<\/strong> built on React \u2014 particularly Next.js<\/strong> and Remix<\/strong> \u2014 do provide the full framework experience: routing, server rendering, data loading, and deployment tooling, all running on React components underneath.<\/p>\n React is primarily a front-end library, but modern React blurs this line. With React Server Components (introduced in React 18 and expanded in React 19), components can run on the server and stream HTML to the client. Next.js uses this extensively \u2014 some components run server-side, others client-side, all written in React.<\/p>\n In React, every UI element is a component<\/strong> \u2014 a JavaScript function that returns JSX (JavaScript XML), a syntax extension that looks like HTML but compiles to JavaScript:<\/p>\n JSX makes component templates readable. Under the hood, the JSX above compiles to Components receive data through props<\/strong> (read-only inputs passed from a parent) and manage internal data through state<\/strong> (mutable values that trigger re-renders when updated):<\/p>\n React maintains a lightweight, in-memory copy of the real DOM called the virtual DOM<\/strong>. When state changes, React:<\/p>\n This “reconciliation” process makes React fast \u2014 it avoids expensive full-page re-renders by updating only what changed.<\/p>\n React 19 (stable since 2024) introduced Server Components<\/strong> as a first-class feature. Server Components run on the server and send rendered HTML to the client \u2014 they have zero JavaScript bundle cost. Client Components continue to run in the browser for interactive elements. This hybrid model lets teams build faster, lighter applications while keeping React’s component model.<\/p>\n Even if you never write React code yourself, understanding React’s component model makes you a better UI designer:<\/p>\n Design UIs 8.6x faster with real React components<\/p>\n UXPin Forge generates layouts from your production React library. Merge lets you refine them with professional design tools. Try it free.<\/p>\n<\/p>\n<\/div>\n Try UXPin Free<\/a>\n<\/div>\n Start with the official React documentation<\/a> (react.dev) \u2014 it was rewritten in 2023 and is widely considered the best React learning resource available. Build small projects (a to-do list, a weather app, a product catalog) to reinforce concepts. Once comfortable, explore Next.js for full-stack React development. If you prefer structured learning, Treehouse<\/a> offers browser-based coding courses including React fundamentals with live instructor support and portfolio-building projects.<\/p>\n Traditional design tools create pixel-based representations of interfaces that developers must recreate from scratch. UXPin Merge<\/a> takes a different approach: it brings your production React components into the design tool so designers work with the actual code<\/em>.<\/p>\n Here is how it works:<\/p>\n This workflow is why enterprise teams report up to a 50% reduction in engineering time when using Merge \u2014 the “translation” step between design and code simply disappears.<\/p>\n React is used for building user interfaces \u2014 primarily for web applications, but also for mobile apps (via React Native), desktop apps (via Electron), and even server-rendered pages (via Next.js). It is especially well-suited for complex, interactive applications with frequently changing data, such as dashboards, social platforms, and e-commerce sites.<\/p>\n React’s core concepts (components, props, state, JSX) can be learned in a few weeks if you already know HTML, CSS, and JavaScript. The broader ecosystem (routing, state management, server rendering) takes longer to master. The official React documentation at react.dev is the best starting point.<\/p>\n JSX (JavaScript XML) is a syntax extension that lets you write HTML-like markup inside JavaScript. It makes component templates more readable and is the standard way to define UI in React. JSX is not valid JavaScript \u2014 it is compiled to The virtual DOM is a lightweight, in-memory representation of the actual browser DOM. When state changes, React creates a new virtual DOM tree, compares it with the previous one, calculates the minimum necessary changes, and applies only those changes to the real DOM. This makes updates fast because React avoids re-rendering the entire page.<\/p>\n Yes. UXPin Merge<\/a> lets designers drag and drop production React components onto a visual canvas, configure props through a properties panel, and arrange layouts \u2014 all without writing code. The output is production-ready JSX that developers can use directly. Forge<\/a> takes this further by generating complete layouts from text prompts.<\/p>\n React Server Components (RSC) are components that run on the server and send rendered HTML to the client. They have zero JavaScript bundle cost, which makes applications faster. RSC was introduced in React 18 and became a stable feature in React 19. Next.js is the primary framework that uses RSC in production.<\/p>\nWhat Is React?<\/h2>\n
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Is React a Framework or a Library?<\/h3>\n
Is React Front-End or Back-End?<\/h3>\n
How React Works<\/h2>\n
Components and JSX<\/h3>\n
function Greeting({ name }) {\n return <h1>Hello, {name}!<\/h1>;\n}<\/code><\/pre>\nReact.createElement('h1', null, 'Hello, ', name, '!')<\/code>.<\/p>\nProps and State<\/h3>\n
import { useState } from 'react';\n\nfunction Counter() {\n const [count, setCount] = useState(0);\n return (\n <div>\n <p>Count: {count}<\/p>\n <button onClick={() => setCount(count + 1)}>\n Increment\n <\/button>\n <\/div>\n );\n}<\/code><\/pre>\nThe Virtual DOM<\/h3>\n
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React Server Components<\/h3>\n
Why React Dominates in 2026<\/h2>\n
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React for Designers: Why It Matters<\/h2>\n
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How to Get Started with React<\/h2>\n
Prerequisites<\/h3>\n
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async\/await<\/code>.<\/li>\nimport<\/code> and export<\/code> syntax.<\/li>\n<\/ul>\nKey Concepts to Learn<\/h3>\n
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useState<\/code>, useEffect<\/code>, useRef<\/code>, useContext<\/code>.<\/li>\nRecommended Learning Path<\/h3>\n
Designing with React Components in UXPin<\/h2>\n
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Frequently Asked Questions<\/h2>\n
What is React used for?<\/h3>\n
Is React hard to learn?<\/h3>\n
What is JSX in React?<\/h3>\n
React.createElement()<\/code> calls by build tools like Babel or the TypeScript compiler.<\/p>\nWhat is the virtual DOM and why does React use it?<\/h3>\n
Can designers use React components without writing code?<\/h3>\n
What are React Server Components?<\/h3>\n