React Knowledge Patch Skill

React Knowledge Patch

Claude Opus 4.6 knows React through 18.x. It is unaware of the features below, which cover React 19.0 through 19.2 (released 2025-10-01).

Index

| Topic | Reference | Key features | |---|---|---| | Server rendering APIs | references/server-rendering.md | cacheSignal, prerender, resume, resumeAndPrerender, Partial Pre-rendering |

`<Activity />`

New component for pre-rendering and preserving state of hidden UI. Replaces conditional rendering with mode-based visibility.

// Instead of: {isVisible && <Page />}
<Activity mode={isVisible ? 'visible' : 'hidden'}>
  <Page />
</Activity>;

Mode behavior

| Mode | Children | Effects | Updates | |---|---|---|---| | visible | Shown | Mounted | Processed normally | | hidden | Hidden | Unmounted | Deferred until React is idle |

When to use

Pre-rendering likely navigation targets (e.g., next page in a wizard)
Preserving state on back navigation (e.g., tab content, scroll position)
Keeping off-screen content ready without the cost of full rendering

Unlike conditional rendering ({show && <Component />}), <Activity> preserves component state and DOM when toggling between modes. Hidden children are deprioritized but not destroyed.

eslint-plugin-react-hooks v6

Now uses ESLint flat config by default.

// eslint.config.js (flat config, v6 default)
import reactHooks from 'eslint-plugin-react-hooks';

export default [
  reactHooks.configs.recommended,
];

For legacy .eslintrc config, change the extends name:

- extends: ['plugin:react-hooks/recommended']
+ extends: ['plugin:react-hooks/recommended-legacy']

Reference Files

| File | Contents | |---|---| | server-rendering.md | cacheSignal for RSC, Partial Pre-rendering (prerender, resume, resumeAndPrerender), Node stream variants |

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