Server-Side Rendering

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.

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.

Flexbox (Flexible Box Layout) is a one-dimensional CSS layout model designed for distributing space and aligning items within a container along a single axis — either horizontal or vertical. It excels at handling dynamic content sizes, centering elements, and creating flexible navigation bars, card rows, and form layouts. Properties like `justify-content`, `align-items`, and `flex-grow` give you fine-grained control over how items share available space.

Shadow DOM is a browser API that allows you to attach a hidden, encapsulated DOM tree to an element, isolating its styles and markup from the rest of the page. This means CSS defined inside a Shadow DOM won't leak out, and external styles won't bleed in. It's the core technology behind Web Components and is used by frameworks to achieve true style encapsulation without CSS naming conventions or tooling.

A Higher-Order Component (HOC) is an advanced React pattern where a function takes a component as input and returns a new enhanced component with additional props or behavior. Common use cases include adding authentication checks, analytics tracking, or data fetching logic to existing components. While HOCs were a primary code reuse pattern in class-based React, custom hooks have largely replaced them in modern functional component code due to their simpler composition model.

A design system is a collection of reusable components, guidelines, and standards that ensure visual and functional consistency across a product or suite of products. It typically includes a component library, design tokens, typography rules, color palettes, and documentation. Design systems bridge the gap between designers and developers, enabling teams to build interfaces faster while maintaining a unified look and feel.