React is a JavaScript library created by Meta (formerly Facebook) for building user interfaces. Rather than a complete framework, React focuses specifically on the view layer - how data is presented to users.
Released in 2013, React revolutionised web development by introducing the concept of reusable components and a declarative programming model. Today, React is the most popular JavaScript library for web development.
Core Concepts
Components: React applications are built from components - reusable pieces of UI that manage their own state and logic. Components range from simple buttons to complex interfaces combining multiple sub-components.
Declarative: React uses declarative syntax where developers describe what the UI should look like for a given state. React handles updating the DOM when state changes, rather than developers manually manipulating the DOM.
Virtual DOM: React maintains a virtual representation of the DOM. When state changes, React calculates the minimal set of actual DOM updates required and applies them efficiently. This dramatically improves performance compared to manually manipulating the DOM.
Unidirectional Data Flow: Data flows downward from parent components to child components. This one-way flow makes applications easier to understand and debug compared to two-way data binding.
Advantages of React
Component Reusability: Building applications from reusable components reduces code duplication and improves maintainability.
Developer Experience: React's syntax (JSX) feels natural to developers. Hot reloading enables seeing changes without page refresh.
Performance: The virtual DOM and React's optimisations enable building responsive applications.
Large Ecosystem: An enormous ecosystem of libraries, tools, and extensions exists for React.
Community: React has a massive, active community providing libraries, tutorials, and solutions to common problems.
JSX Syntax
React applications are typically written using JSX - a syntax extension that looks like HTML but compiles to JavaScript. JSX allows writing UI descriptions that look familiar to developers experienced with HTML, whilst having the full power of JavaScript.
State and Props
Props: Components receive props (properties) from parent components. Props are read-only - child components cannot modify props passed from parents.
State: Components can have internal state that changes over time. When state changes, React re-renders the component and its children.
Understanding the distinction between props and state is fundamental to React development.
Hooks - Modern React Development
React Hooks, introduced in 2018, revolutionised how React developers write components. Hooks allow using state and other features in functional components without writing class components.
Common hooks include useState for managing component state, useEffect for side effects like fetching data, and useContext for accessing context values.
React Ecosystem
Next.js: A framework built on React providing server-side rendering, static generation, and simplified routing.
State Management: Redux, Zustand, and MobX manage application state across multiple components.
Routing: React Router provides client-side routing for single-page applications.
UI Libraries: Material-UI, Chakra UI, and others provide pre-built components.
Single-Page Applications
React is ideal for building single-page applications (SPAs) - applications that load once and update dynamically without full page reloads. SPAs provide responsive, app-like experiences in the browser.
Server-Side Rendering
Whilst React traditionally renders in the browser, modern tools like Next.js enable server-side rendering - rendering React components on the server before sending HTML to browsers. This improves performance and SEO.
Performance Considerations
React applications are generally fast due to the virtual DOM and React's optimisation strategies. However, poorly written React code can have performance issues. Understanding React's rendering model is crucial for writing performant applications.
Testing React Applications
React applications are testable using tools like Jest (testing framework), React Testing Library (component testing), and Cypress (end-to-end testing).
Mobile Development with React
React Native extends React's concepts to mobile development, allowing developers experienced with React web to build native mobile applications using React principles.
Learning React
React's documentation is excellent and the community provides extensive learning resources. Developers with JavaScript knowledge can learn React relatively quickly.
The React Ecosystem Advantage
One of React's major advantages is its ecosystem. Almost any functionality needed is available as a library. This abundance means less time building infrastructure and more time building features.
Comparison with Other Frameworks
Vue and Angular are alternative JavaScript frameworks. React's market share, ecosystem size, and job market make it the most popular choice for new projects.
Enterprise Adoption
Major organisations use React at scale - Netflix, Uber, Airbnb, and countless others. React's capability to handle massive, complex applications is well-proven.
The Future of React
The React team continues improving React. Recent work on concurrent rendering aims to further improve performance. Server components promise to bring server-side benefits to React development.
For building modern, responsive user interfaces on the web, React is an excellent choice. Its component model, ecosystem, and proven success at scale make it a pragmatic choice for organisations building web applications.