One small, tested place for everything React Native styling libraries read from React's private fiber tree.
Built for Unistyles and Uniwind Pro.
React 19 · React Native 0.86 – 0.87 · iOS + Android · Hermes-first · MIT
Unistyles and Uniwind both do something React Native doesn't officially support: they update the native shadow tree without a React render. Theme switches, breakpoints and insets reach native views in a single commit. To do that, both read React's private fiber fields: __internalInstanceHandle, stateNode.node, memoizedState, return, alternate and more.
Until now, each library kept its own copy of those reads. They drifted apart, and both had bugs that only show up on real apps.
unifiber is the one module that knows what a fiber looks like. It answers questions such as "which native view is this ref?", "is it hidden, and why?" and "what must refresh?". It's tested against React Native's own components and Unistyles' real code. A daily CI run against React Native nightly catches changes to React's internals before they ship.
Fiber and Reanimated are plain objects. A Host is a native view's creation fiber behind an opaque type: free to keep, and stable, so the same view is always the same Host (=== and WeakMap keys work).
getHostFor(ref) |
Native-view refs, RN composites (ScrollView, FlatList / SectionList / VirtualizedList, ImageBackground, KeyboardAvoidingView, RefreshControl), and class components that render their view directly (Button on Android). Any other class component gives the first native view it renders, which may not be the one you styled. Call once per link and keep the result. |
getShadowNodeFor(ref) |
Hot path when you don't keep a Host. |
getHostForInstanceHandle(handle) |
For fibers handed back from C++ (ShadowNodeFamily::getInstanceHandle). |
getContentContainerFor(ref) |
ScrollView / list content container, through RN's public getInnerViewRef(). |
getShadowNode(host) |
The node in React's stateNode.node wrapper. |
getShadowNodes(host, out?) |
Every node React may diff against or re-attach: one after a commit, two while a render is in flight. |
getNativeTag(host) |
undefined once the view has unmounted. |
getParentHost(host) |
The nearest native view above (ActivityIndicator's wrapper, on both platforms). |
patchRenderedProps(host, patch) |
Replaces React's diff baseline on both halves. The only write, used by Uniwind's baseline. |
Hidden state
isHidden(host) |
Inside a Suspense fallback, a frozen screen or a hidden <Activity>: suspend instead of unlinking. Also right inside a ref cleanup, where React has not switched the committed tree yet. |
isSuspended · isFrozen · isInHiddenActivity |
Why. Frozen means react-freeze (react-native-screens freezeOnBlur, react-navigation). |
collectVisibleAncestors(hosts, visit) |
Batch refresh. Each visible native view from hosts up to the root, visited once, in one shared pass. |
collectAncestors(hosts, visit) |
The same walk, with hidden views included. These are the semantics of Uniwind's collectHostNodes today. |
verify(host, expected) |
Style keys React would re-send, i.e. undo, on this view's next render. |
getOwners(host) |
Development builds only: the components that created the view, e.g. ['ProfileCard', 'ProfileScreen']. |
getCreationStack(host) |
Development builds only: where the JSX was written, for Metro to symbolicate. |
Reanimated's AnimatedComponent keeps its own copy of a view's style for CSS transitions, so a native-only theme change gets overridden. The adapter keeps that copy in sync, so the theme change animates instead.
const owners = Fiber.createOwnerRegistry({
name: 'unistyles',
epoch: () => themeVersion, // bump on every runtime change
contexts: [ScopedThemeContext],
contextKey: (_ctx, scope) => scope?.name, // stable scopes are renamed in place
resolve: (props, read) => freshStyles(props, read(ScopedThemeContext)),
}, [Reanimated.cssAdapter], warnOnce)
owners.link(host) // in the link path: ~86 ns for a plain view
owners.refresh(hosts) // after a native-only updateHidden views (a frozen screen, Suspense, a hidden <Activity>) are refreshed too, so a transition-only view shows the new value when it's revealed. Trade-off: a view that also has a keyframe animation (animation* keys) or pseudo-style values isn't refreshed while hidden. After it's revealed, it transitions from the pre-hide value to the new one, then settles correctly. Reanimated registers animations and pseudo-styles again on update, and React runs no componentWillUnmount for a subtree deleted while hidden, so refreshing them would leak.
An adapter that throws is switched off for the session and reported once. Private Reanimated fields are pinned by a contract test against the 4.5.1 and 4.7.0 sources.
| React | 19.2, and 19.3.1 with RN nightly (fiber tags pinned for 19.x) |
| React Native | 0.87.1, 0.86.3 · iOS, Android · development and production. CI also runs React Native nightly (main) every day; 0.89.0-nightly-20261016 passes |
| Reanimated | 4.5.1, 4.7.0 |
| Unistyles | 3.5.3 and main (its real code runs in the suite) |
| Uniwind | its lookups copied verbatim into the suite |
| Engine | Hermes (legacy Hermes benchmarked) |
MIT