React.JS Developer

Markup as expressions, conditional rendering and fragments - UI as a function of state.

Data down, events up; children and slot patterns - assembling screens from small parts.

Rendering collections, stable keys and empty states - where subtle UI bugs are born.

Breaking a mock into a component tree and deciding where state lives - the design skill behind clean apps.

State as a snapshot, updater functions and batching - why 'it's one behind' happens and how to fix it.

Inputs bound to state, validation and submission - the highest-traffic pattern in product code.

Moving state to the closest common parent, and recognising when you actually need context.

State machines for complex updates - predictable transitions instead of scattered setters.

Synchronising with external systems: dependencies, cleanup and strict-mode double-invoke - and the many effects that shouldn't exist.

App-wide values (theme, auth) without prop drilling - and its re-render cost.

Mutable boxes and imperative DOM access (focus, scroll) - leaving the declarative world safely.

Extracting reusable logic (useLocalStorage, useDebounce) - the composition unit of modern React.

Routes, params, nested layouts and redirects with React Router - URL as application state.

React Query mindset: queries, invalidation, optimistic updates - replacing useEffect-fetch spaghetti.

Suspense-ready thinking: every remote read has three extra states users will see.

Next.js: server components, file routing and when an SPA isn't the right default.

Why components re-render; memo, useMemo and useCallback - measured with the Profiler, not guessed.

lazy + Suspense and route-level splitting - shipping less JavaScript to first paint.

Testing Library: test behaviour users see, not implementation details.

Typing props, events, children and hooks - the professional default.

Catching render crashes gracefully and escaping the DOM tree for modals and toasts.

Declarative loading boundaries, transitions and streaming - the model modern frameworks build on.

Zustand, Redux Toolkit and Jotai - when component state stops scaling and which tool fits which shape of app.

CSS Modules vs Tailwind vs component systems (Radix, shadcn/ui) - accessible primitives over reinvented wheels.

react-hook-form + zod: performant forms with one schema validating client and server.

Motion (Framer Motion) for enter/exit and layout animation - polish that respects reduced-motion.

Take the OneRoadmap React certification - verified proof recruiters can check.