Textbook in PDF format Battle-tested strategies and real-world insights from a Technical Lead who has conducted 350+ front-end interviews. This book is created for experienced developers who want to confidently navigate React.js interviews and demonstrate not only knowledge but also the ability to apply it in practice. Modern companies evaluate candidates based on how deeply they understand architecture, state management, security, accessibility, performance, and the practical workings of large applications. Simple answers are not enough—mature engineering thinking is required. The book is written by Kristian Velkov — a Front-end lead, mentor, author, and Docker Captain, who has conducted over 350 technical interviews. It contains practical strategies, real questions, and approaches used by leading companies when assessing Middle and Senior developers. What You Will Learn – React Security: preventing XSS and CSRF, secure data handling, route protection, and authentication. – Web Accessibility (a11y): applying WCAG, using ARIA, proper keyboard navigation, creating accessible components. – React with TypeScript: advanced types for components, props, events, and hooks; using Partial, Pick, Omit, Record. – Routing: React Router and TanStack Router, nested and protected routes, layout routes, handling parameters and query strings. – Global State: Context API, Redux Toolkit, Zustand, MobX; preventing unnecessary re-renders; scaling state in large applications. – Data Fetching and Caching: fetch, Axios, SWR, TanStack Query; pagination, background refetching, optimistic updates, error handling. – GraphQL and API: differences between GraphQL and REST, queries and mutations, integrating Apollo Client, optimization and security. – Testing and Testing Strategies: Jest, React Testing Library, Cypress; API mocking, simulating user behavior, testing complex logic. – Server-Side Rendering and Next.js: differences CSR/SSR/SSG/ISR, building high-performance Next.js applications, caching, dynamic routes, API routes. – Microfrontends and Architecture: application splitting, shared components and state, performance and security in microfrontend environments. – Deployment and CI/CD: containerizing React applications with Docker, CI/CD on GitHub Actions and GitLab, deployment on Vercel, Netlify, and AWS. Who This Book Is For Mid-level Developers: helps to systematize knowledge, master best practices, and prepare for mid-level interviews. Senior Developers and Technical Leads: covers architecture, complex patterns, performance, and real-world scenarios required for higher responsibility roles. Structure of Each Question Detailed Answer: a thorough explanation of the concept. Brief Answer: a convenient summary for quick review. Code Examples: practical solutions in TypeScript. Additional Materials: links to documentation and resources for in-depth study. This book will be your strategic advantage—whether you're searching for a new position, preparing for a promotion, or furthering your career development. It will provide you with the knowledge, structure, and confidence needed to stand out in the market and successfully navigate React.js interviews at Mid-Level and Senior levels