Guide / React coverage

React coverage

Each React API, and what brust does with it: lowered to native code, rendered once as static markup, or left to React as an island. Every row is a case the test battery builds and checks.

Summary

58 entries from the React reference (react.dev, fetched 2026-10-13): 11 native, 9 static, 30 island, 3 partial, 5 not applicable.

Native: compiled to a template the server fills and a binding the browser updates; no React in the browser.
Static: rendered once; the page ships the markup and nothing else.
React island: the component runs in React, rendered by the worker and hydrated in the browser. The rest of the page keeps its tier.
Partial: some shapes of the API are native or static and others are islands; the note says which.
Not applicable: the API has no meaning in brust (there is no Server Components runtime).

Hooks

Entry	Tier	Note
`useActionState`	React island	any hook outside the supported hooks `hook-unsupported`
`useCallback`	Native
`useContext`	React island	`hook-unsupported`
`useDebugValue`	React island	any hook outside the supported hooks `hook-unsupported`
`useDeferredValue`	React island	any hook outside the supported hooks `hook-unsupported`
`useEffect`	Native	effect-deps: the deps array is complete, so no warning () `effect-deps`
`useEffectEvent`	React island	any hook outside the supported hooks `hook-unsupported`
`useId`	Static	useId: the server seeds _id0 (); no state or handler, so the tier is static
`useImperativeHandle`	React island	any hook outside the supported hooks `hook-unsupported`
`useInsertionEffect`	React island	any hook outside the supported hooks `hook-unsupported`
`useLayoutEffect`	Native
`useMemo`	Native
`useOptimistic`	React island	any hook outside the supported hooks `hook-unsupported`
`useReducer`	React island	`hook-unsupported`
`useRef`	Native
`useState`	Native
`useSyncExternalStore`	React island	`hook-unsupported`
`useTransition`	React island	startTransition is outside the supported set `hook-unsupported`

Components

Entry	Tier	Note
`<Activity>`	React island	<Activity mode> `external-component` `island-children`
`<Fragment>`	Static	static fragment root: no <brust-host>, no warning (gaps L8)
`<Profiler>`	Partial	island: d-profiler-bare; refused: d-profiler `island-prop` `external-component` `island-children`
`<StrictMode>`	React island	`external-component` `island-children`
`<Suspense>`	React island	fixed: a dynamic import() is a dynamic-import fallback, not a printer panic `dynamic-import` `external-component` `island-children` `jsx-expression` `local-component`
`<ViewTransition>`	React island	`external-component` `island-children`

APIs

Entry	Tier	Note
`act`	Not applicable	A test helper; it has no runtime meaning in a brust page. Importing it changes nothing about a component.
`addTransitionType`	React island	addTransitionType inside startTransition `hook-unsupported`
`cache`	Static	cache()
`cacheSignal`	Static	cache(): the call is a precompute job on the server
`captureOwnerStack`	React island	captureOwnerStack in a handler `hook-unsupported`
`createContext`	React island	createContext provider `member-tag` `jsx-expression`
`experimental_taintObjectReference`	React island	`hook-unsupported`
`experimental_taintUniqueValue`	React island	`hook-unsupported`
`lazy`	React island	fixed: a dynamic import() is a dynamic-import fallback, not a printer panic `dynamic-import` `external-component` `island-children` `jsx-expression` `local-component`
`memo`	Partial	native/static: b-memo; island: d-memo-state `default-export-shape`
`startTransition`	React island	startTransition is outside the supported set `hook-unsupported`
`use`	React island	`hook-unsupported`

react-dom hooks

Entry	Tier	Note
`useFormStatus`	Partial	native/static: c-useformstatus-child; island: c-useformstatus; known gap: the root is static and Submit is an island, but the <form> is not a React form, so pending never becomes true; the root should be react `hook-unsupported`

react-dom components

Entry	Tier	Note
`<form>`	Native	<form onSubmit>; known gap: a function action becomes a precompute value that the url_ok guard drops, so the form renders without an action and submits nowhere; it should fall back to react
`<input>`	Native	controlled <input>
`<select>`	Native	controlled <select>
`<textarea>`	Native	controlled <textarea>
`<title>`	Static	<title> in a component body
`<meta>`	Static	<meta> in a component body
`<link>`	Static	<link rel=stylesheet> in a component body
`<style>`	Static	<style> element
`<script>`	Static	<script async src>

react-dom APIs

Entry	Tier	Note
`createPortal`	React island	`browser-global`
`flushSync`	Native	flushSync in a handler; known gap: compiles native but the client chunk imports react-dom (a native chunk must contain no react import); it should fall back to react
`preconnect`	React island	preconnect in render `body-shape`
`prefetchDNS`	React island	prefetchDNS in render `body-shape`
`preinit`	React island	preinit in render `body-shape`
`preinitModule`	React island	preinitModule in render `body-shape`
`preload`	React island	preload in render `body-shape`
`preloadModule`	React island	preloadModule in render `body-shape`

Server

Entry	Tier	Note
`'use client'`	Not applicable	No directives: every component is classified by the compiler. The directive is ignored with a warning. `use-client-leftover`
`'use server'`	Not applicable	No directives: server work is an Elysia app under `[actions]`, or a loader/job. A `'use server'` function is not a server function here.
`Server Components`	Not applicable	No Server Components: a loader and the compiled jobs are the server half, components render to HTML on the Rust server.
`Server Functions`	Not applicable	No Server Functions: call an `[actions]` route (`@brust/core/actions`) instead.

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