Dictionary

Retrieval-Augmented Generation (RAG) is a technique that enhances LLM responses by retrieving relevant documents from an external knowledge base before generating an answer. This allows the model to ground its output in up-to-date, domain-specific information rather than relying solely on its training data. RAG is widely used in enterprise chatbots, documentation assistants, and search-powered AI applications.

React Hooks are functions (like `useState`, `useEffect`, `useMemo`, `useCallback`) that let you use state, side effects, and other React features inside functional components without writing classes. Introduced in React 16.8, they fundamentally changed how React applications are structured by enabling logic reuse through custom hooks. Hooks must follow two rules: they can only be called at the top level of a component, and only inside React function components or other hooks.

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.

The React Native New Architecture is a fundamental rewrite of React Native's internals, replacing the asynchronous bridge with a JavaScript Interface (JSI) that enables direct, synchronous communication between JavaScript and native code. It consists of three pillars: Fabric (a new rendering system), Turbo Modules (a faster native module system), and Codegen (automatic type-safe native code generation from JS specs). This architecture significantly improves performance, reduces startup time, and enables concurrent rendering features from React 18.

React Navigation is the most widely used routing and navigation library for React Native applications. It provides stack, tab, and drawer navigators that mimic native navigation patterns on both iOS and Android, with smooth transitions and gesture support. Its JavaScript-based approach means navigation logic is fully customizable, and it integrates with deep linking, authentication flows, and state persistence out of the box.

React Server Components (RSC) are components that render exclusively on the server and send only their HTML output to the client, with zero JavaScript bundle impact. They can directly access databases, file systems, and backend services without API endpoints. Combined with Client Components (marked with `'use client'`), RSC enables a hybrid architecture where interactive parts ship JavaScript while static or data-heavy parts remain server-only. Next.js App Router uses RSC as its default component model.

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.

Redux is a predictable state management library that stores the entire application state in a single immutable store, updated exclusively through dispatched actions and pure reducer functions. Redux Toolkit (RTK) is now the recommended way to use Redux, dramatically reducing boilerplate with utilities like `createSlice` and `createAsyncThunk`. While Redux remains popular in large enterprise applications that benefit from strict unidirectional data flow and time-travel debugging, lighter alternatives like Zustand have gained ground for simpler use cases.

Reinforcement learning (RL) is a machine learning paradigm where an agent learns optimal behavior by interacting with an environment and receiving rewards or penalties. RLHF (Reinforcement Learning from Human Feedback) is a key technique used to align LLMs with human preferences, making their outputs more helpful and safe. RL is also behind breakthroughs in game-playing AI and robotics.

Responsive design is an approach to web development where layouts, images, and UI elements adapt fluidly to different screen sizes and devices. It relies on flexible grids, media queries, and relative units like `rem`, `%`, and `vw` to ensure a consistent experience from mobile phones to large monitors. Modern responsive design increasingly uses CSS Container Queries and intrinsic sizing techniques to create components that respond to their own container rather than the viewport.