Semantic HTML

A toast notification is a small, non-intrusive message that appears briefly on screen — usually at the top or bottom — to provide feedback about an action without interrupting the user's workflow. Unlike modals, toasts auto-dismiss after a few seconds and don't require user interaction. They are commonly used to confirm saves, report errors, or show status updates. Accessible implementations include ARIA live regions so screen readers announce the message.

Atomic Design is a methodology by Brad Frost for creating design systems by breaking interfaces into five hierarchical levels: atoms (basic HTML elements), molecules (simple component groups), organisms (complex UI sections), templates (page-level layouts), and pages (specific instances with real content). This approach provides a consistent mental model for organizing component libraries in React, React Native, or Flutter projects and ensures systematic scalability of the UI.

Reconciliation is React's algorithm for comparing the previous and current Virtual DOM trees to determine the minimum number of changes needed to update the actual DOM. React uses heuristics like element type comparison and the `key` prop to efficiently decide whether to update, replace, or remove DOM nodes. Understanding reconciliation explains why unique `key` props on list items matter — without them, React can't reliably track which items changed, leading to bugs and poor performance.

Next.js is a full-stack React framework by Vercel that provides server-side rendering, static site generation, API routes, file-based routing, and built-in optimizations out of the box. Its App Router (introduced in v13) uses React Server Components by default, enabling a new paradigm of server-first rendering with selective client-side interactivity. Next.js has become the de facto standard for production React applications due to its performance optimizations, developer experience, and deployment flexibility.

Server-Side Rendering (SSR) is a technique where web pages are rendered to HTML on the server for each request, rather than relying on client-side JavaScript to build the page in the browser. SSR provides faster initial page loads and better SEO since search engines receive complete HTML content. Modern SSR in frameworks like Next.js supports streaming, allowing the server to progressively send HTML chunks as they become ready rather than waiting for the entire page to render.

CSS Modules are CSS files where all class names are locally scoped by default, meaning they're automatically transformed into unique identifiers at build time to prevent naming collisions. You import them into your JavaScript as an object and reference classes like `styles.button` instead of plain strings. This approach is natively supported by bundlers like Webpack, Vite, and Next.js, offering style isolation without the runtime overhead of CSS-in-JS.