React & Next.js

Master React and Next.js for software engineering interviews, covering component patterns, hooks, state management, App Router, data fetching, authentication, performance, and testing. Session 1: React Fundamentals React's mental model is a function from state to UI: . Every re-render is React calling your component function again with new state or props. JSX JSX is syntactic sugar over . The JSX transformer (Babel/SWC) converts it at build time. Components and Props State with useState Controlled vs Uncontrolled Inputs Interview Insight "Why shouldn't you mutate state directly?" — React uses reference equality to detect changes. If you mutate an object in place (obj.name = 'new'), the reference is unchanged, React sees no change, and no re-render occurs. Always return new objects/arrays from state updates. Java Implementation Python Implementation