Headless UI

React Native is a framework for building native mobile applications for iOS and Android using React and JavaScript/TypeScript. Unlike hybrid approaches that render in a WebView, React Native maps React components to actual native platform UI elements, providing native look, feel, and performance. Its "learn once, write anywhere" philosophy allows web developers to leverage their React knowledge for mobile development while still accessing platform-specific APIs when needed.

CSS Grid is a two-dimensional layout system that lets you define rows and columns simultaneously, making it ideal for complex page layouts. Unlike Flexbox which works in one axis at a time, Grid allows you to place items precisely in both horizontal and vertical directions using named areas or line numbers. Features like `grid-template-areas`, `auto-fill`, and `minmax()` make it possible to create responsive layouts with minimal code.

Progressive enhancement is a web development strategy that starts with a baseline of functional HTML content accessible to all browsers, then layers on CSS styling and JavaScript interactivity for more capable environments. This approach ensures that core functionality works everywhere, while users with modern browsers get a richer experience. It contrasts with graceful degradation, which starts with the full experience and tries to handle failures.

A task runner is a tool that automates repetitive development tasks like compiling code, running tests, minifying assets, and restarting servers. Early web task runners like Grunt and Gulp defined workflows as JavaScript code, while modern approaches use npm scripts, Turborepo, or Nx for monorepo-aware task orchestration. Task runners form the foundation of local development automation, ensuring every team member runs tasks consistently.

The Virtual DOM is a lightweight in-memory representation of the actual browser DOM that React uses to optimize UI updates. When state changes, React creates a new Virtual DOM tree, compares it with the previous one through a process called reconciliation, and calculates the minimal set of real DOM mutations needed. This batching and diffing approach avoids expensive direct DOM manipulation and was a key innovation that made React's declarative programming model performant.

Internationalization (i18n) is the process of designing software so it can be adapted to different languages, regions, and cultures without code changes. This involves externalizing strings, supporting right-to-left (RTL) layouts, handling date/number/currency formatting, and accommodating text expansion. Libraries like react-intl, next-intl, and i18next provide the infrastructure for managing translations and locale-aware formatting in JavaScript applications.