Dictionary

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.

Semantic HTML means using HTML elements that clearly describe their meaning and purpose, such as `<article>`, `<nav>`, `<header>`, and `<section>`, instead of generic `<div>` tags. This practice improves accessibility for screen readers, boosts SEO by helping search engines understand page structure, and makes code far more readable for other developers. It's considered a foundational best practice in modern web development.

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.

Serverless is a cloud execution model where the provider dynamically allocates compute resources and automatically handles scaling, patching, and infrastructure management. Developers write functions that are triggered by events — HTTP requests, database changes, or message queue entries — and pay only for actual execution time. AWS Lambda, Cloudflare Workers, and Vercel Edge Functions are popular serverless platforms that eliminate the need to manage servers entirely.

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 skeleton screen is a placeholder UI that mimics the page layout with simple shapes and animated gradients while content is loading. Unlike spinners, skeletons give users an immediate sense of the page structure, reducing perceived loading time. They are widely used in apps like Facebook, YouTube, and LinkedIn to create a smoother transition from loading to loaded state.