new·The score now tells you which way it movedA brain's exam only ever grows: its own material writes questions, and so does every question a real caller asked and did not get answered. The score is a percentage over that growing set, so a brain that learned more could post a smaller number — and this week three did. One of them answered two MORE questions than the week before and showed eighteen points less. Printed as a single percentage, that reads as decline to a reader and as punishment to anyone who contributes material.all news →
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explore / Web & frontend / mozg / React

React · API reference

Answer questions about the React API exactly as specified: every hook, component, directive and API in react and react-dom with its signature, parameters, return value and usage rules.

1,769 notes · updated 2026-08-15 · trained 73%

since last sitting: +49 newly passed — this brain is learning · the verified changelog →

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Ask it things like

answers 49/70 on its latest exam
What is the exact signature of useState, including parameter type and return type?Core Hooks: Signatures✓
What does useEffect's cleanup function return and when is it called?Core Hooks: Signatures✓
What is the signature of useTransition and what does it return?Core Hooks: Signatures✓
What is the signature of useRef and what must you do to access the value?Core Hooks: Signatures✓
What is the signature of useReducer and what types does it accept?Core Hooks: Signatures✓
What is the signature of createContext and what does it return?Context API✓
What is the signature of React.memo and when should you use it?Core Components✓
What is the signature of forwardRef and what does it do?Core Components✓

What it can answer

70 coverage checks
73%
Answers 49 of the exam's 70 questionsIt answers 49 questions, 49 more than last time, out of an exam that grew by 70.Nothing it used to answer has stopped working.
▲Core Hooks: Signatures11 / 12
▲Core Components6 / 8
▲DOM Rendering5 / 6
✓Ref Management5 / 5
▲DOM Components: Form Inputs4 / 7
▲Event Handlers4 / 8
▲Server-Side Features3 / 5
▲DOM Components: Rendering2 / 3
▲DOM Components: Styling2 / 3
▲Metadata & Assets2 / 3
▲Server Rendering2 / 5
▲Context API1 / 2
✓Deprecated / Removed1 / 1
✓OptionalAdvanced Hooks1 / 1
✕Optional Advanced Hooks0 / 1
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Attacks survived

re-run weekly · 2026-08-11
✓gate-battery12/12 known hostile payloads caught by the ingest gate
✓injection-corpusevery active note scanned — no steering language
✓secret-corpusevery active note scanned — no keys or credentials

heuristic scans against known attack classes — measured and dated, not a promise of unpoisonability

Inside

  • React 18 introduces new hooks in working group · core hook signatures
  • Suspense enables streaming server rendering · server rendering
  • React 18 release features and concurrent renderer · react
  • createRoot API migration from ReactDOM.render · react-dom/createroot
  • React 18 new features: automatic batching, startTransition, streaming server renderer · react
  • Concurrent rendering in React 18 · react
  • React 18 release timeline · react
  • React 18 upgrade is opt-in with gradual adoption strategy · react
  • React 18 alpha releases on npm · react
  • Apps not using servers or React Server Components are unaffected · server-side features
  • Vulnerable React Server DOM packages and versions · server-side features
  • CVE-2025-55182: React Server Components RCE vulnerability · server-side features
  • Vulnerability applies to apps without explicit Server Function endpoints · server-side features
  • Fixed versions for CVE-2025-55182 · server-side features

Licence

CC BY-NC-SA 4.0

Use it, copy it, build on it, with credit. Selling it is not allowed.