Styled Components

Storybook is an open-source tool for building and testing UI components in isolation, outside of your main application. Developers define "stories" — different states and variations of a component — which are rendered in a dedicated browser-based workshop. It supports React, Vue, Angular, and other frameworks, making it invaluable for component documentation, visual regression testing, and collaboration between designers and developers.

Blue-green deployment is a release strategy that maintains two identical production environments — "blue" (current) and "green" (new version). Traffic is switched from blue to green only after the new version passes all health checks, enabling zero-downtime releases. If issues are detected, traffic can be instantly routed back to the blue environment, making rollbacks trivial and fully automated.

Focus management is the practice of controlling which element receives keyboard focus in a web application, especially during dynamic content changes. When a modal opens, focus should move into it; when it closes, focus should return to the trigger element. Proper focus management is essential for keyboard and screen reader users, and involves techniques like focus trapping, roving tabindex, and programmatic focus with `element.focus()`.

Tree shaking is a dead code elimination technique used by modern bundlers like Webpack, Rollup, and esbuild to remove unused exports from the final JavaScript bundle. It relies on the static structure of ES module `import`/`export` syntax to determine which code is actually referenced and safely discard the rest. For tree shaking to work effectively, libraries must use ESM format and avoid side effects in their module initialization, which is why the `sideEffects` field in `package.json` matters.

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.

Breadcrumb navigation is a secondary navigation pattern that shows the user's current location within a site hierarchy as a trail of links (e.g., Home > Products > Shoes). It helps users understand where they are and quickly navigate back to parent pages without relying on the browser's back button. Proper implementation uses an ordered list within a `<nav>` element with `aria-label="Breadcrumb"` for accessibility.