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React

React practice

State updates

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Why doesn't the list update after this runs?

items.push(newItem); setItems(items);

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The mental model behind hooks and re-renders

The React model senior frontend interviews probe — components and props/state, the hooks (useState, useEffect, useMemo, useCallback, useRef, useReducer) and the rules that govern them, reconciliation and why keys matter, what actually triggers a re-render, performance (memo, lifting state, Suspense, transitions), and the classic gotchas (stale closures, index keys, direct mutation). Core hooks are version-stable; React 18/19 features are flagged. Part of the Developer track.

• Meets you at your level — never too easy, never too hard.

• Adapts every question to how you’re doing.

• Tracks your level over time. Skill practice, not a test.

New here? Read the React guide

A free 17-minute primer — the mental model, the mistakes beginners make, and what to practice first.

Curriculum

290 concepts across 28 chapters, from foundations through advanced practice — each one a concept the adaptive question bank can teach and test.

A. JSX and describing the UI

B. Props and composition

C. State: a component's memory

D. Render, commit, and reconciliation

E. Updating objects and arrays immutably

F. Choosing, lifting and sharing state

G. Reducers

H. Context

I. Refs and the DOM

J. Effects: synchronizing with external systems

K. You might not need an Effect

L. Rules of React and custom Hooks

M. Performance, memoization and the Compiler

N. Transitions, deferred values and external stores

O. Suspense, lazy and the use Hook

P. Forms, Actions and optimistic UI

Q. react-dom: events, portals and resources

R. Client roots, hydration and StrictMode

S. Server rendering and static prerendering

T. Server Components and Server Functions

U. Error boundaries, class components and testing

V. Client-side routing

W. State and server-state libraries

X. Testing React components

Y. Accessibility in React

Z. Styling approaches

AA. Typing a React app

AB. The Rules of React, enforced — eslint-plugin-react-hooks

View the full curriculum →

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React on exams

React is one of the skills tested on this exam. Each prep page lays out what the real test covers and where this skill fits.

Frontend interview

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