React.js

/riˈækt/

noun … “building user interfaces one component at a time.”

React.js is a JavaScript library for building dynamic, interactive user interfaces, primarily for web applications. Developed by Facebook, React emphasizes a component-based architecture where UIs are broken down into reusable, self-contained pieces. Each component manages its own state and renders efficiently when data changes, using a virtual representation of the DOM to minimize direct manipulations and improve performance.

Key principles of React.js include:

• Component-Based Structure: Interfaces are composed of modular components that encapsulate structure, style, and behavior.
• Virtual DOM: React maintains a lightweight copy of the DOM in memory, allowing it to compute minimal updates to the real DOM when state changes, improving performance.
• Unidirectional Data Flow: Data flows from parent to child components, making state changes predictable and easier to debug. Often paired with Flux or Redux for state management.
• JSX Syntax: React uses JSX, a syntax extension combining JavaScript and HTML-like markup, to describe component structure declaratively.

React.js is closely connected with multiple web development concepts. It integrates with JavaScript for dynamic behavior, leverages Flux or Redux for structured state management, and interfaces with backend APIs (like Fetch-API or Node.js) to render real-time data. React also underpins many modern frameworks such as Next.js for server-side rendering and static site generation.

Example conceptual workflow for using React.js:

define reusable components for UI elements
manage component state and props for dynamic data
render components to the virtual DOM
detect state changes and update only affected parts of the real DOM
connect components to APIs or backend services as needed

Intuitively, React.js is like building a LEGO model: each piece is independent but fits seamlessly with others. When a piece changes, only that piece needs adjustment, allowing developers to create complex, responsive interfaces efficiently, maintainably, and with predictable behavior.