react-native-worklets

Key changes

Networking on Worklet Runtimes in Bundle Mode

Worklet Runtimes created in Bundle Mode now ship a standalone networking module: XMLHttpRequest, Blob, FileReader, fetch (whatwg), Headers, Request, Response, FormData, AbortController and AbortSignal. It replaces the earlier networking preview and its FETCH_PREVIEW_ENABLED feature flag. createWorkletRuntime accepts a new enableNetworking option, which defaults to true and is forced off on runtimes without the Event Loop.

• Worklets: networking module with XMLHttpRequest

• Worklets: add Blob and FileReader to the networking module

• Worklets: add fetch to the networking module

• Worklets: add FormData to the networking module

• Worklets: add AbortController to the networking module

• Worklets: add the enableNetworking runtime option

OXC port of the Worklets Babel plugin

The Worklets Babel plugin has a Rust port built on OXC for Bundle Mode. It is available as react-native-worklets/plugin-oxc/babel, with prebuilt binaries for macOS, Linux and Windows on x64 and arm64.

• Worklets: port babel plugin to oxc

Fixed-type Synchronizable

createSynchronizable accepts a new fixedType option. A fixed-type Synchronizable holds a number or a boolean without serialization and exposes setDirty, a non-exclusive write that doesn't wait for other setDirty calls. On the C++ side Synchronizable is now an interface over std::variant values with a SynchronizableDynamic implementation, and several races on exotic architectors and lock leaks in the dynamic implementation are fixed.

• Worklets: fixed-type Synchronizable

• Worklets: add setDirty to the Synchronizable interface

• Worklets: make Synchronizable value access atomic

• Worklets: release the Synchronizable lock when a setter throws

Faster startup

The native side of WorkletsModule is created on a background thread as soon as the module is created, so installTurboModule only attaches it to the RN Runtime. In Bundle Mode the bundle is evaluated on the UI Worklet Runtime on a background thread while the RN Runtime evaluates it, instead of on the JS thread in start.

• Worklets: initialize the native module ahead of time

• Worklets: start the UI runtime in Bundle Mode ahead of time

Hermes microtask queue on Worklet Runtimes

Worklet Runtimes use the built-in Hermes microtask queue instead of a custom JS implementation.

Removed SerializableInitializer (SerializableHandle)

The Serializable handle is gone: SerializableInitializer, createSerializableInitializer and the __init clone path are removed, and makeShareable serializes its value eagerly into a retaining Serializable. RetainingSerializable caches its value per runtime. Serializable::ValueType::HandleType stays in the Compat Stable API enum for ABI compatibility and extractSerializable throws for it.

• worklets: per-runtime cache in retainingSerializable

Leaner Babel plugin output

Worklet closures are stored as arrays instead of objects, closure-free worklets are exported directly in Bundle Mode without factory wrappers, and implicit worklet context objects are removed. navigator is a known global, so worklets resolve it on their own runtime instead of capturing the main runtime's object by closure.

• Worklets: treat navigator as a known global in the Babel plugin

• chore(rnre+worklets) - less worklets/serialization on run

iOS Swift Package Manager support

Worklets can be integrated on iOS through Swift Package Manager via Package.swift and SPM integration metadata in react-native.config.js. The nightly compatibility check builds the app via SPM on React Native >= 0.87.

• rnre+worklets: add support for SPM

Safer Worklet Runtime teardown

Destroying a Worklet Runtime now acquires the runtime mutex first, so a synchronous call in flight on another thread finishes, discarded results of synchronous calls are destroyed under the lock, and pending jobs of the async queue and event loop are aborted under the lock instead of destroying their JSI handles on an unrelated thread.

• Worklets: acquire the runtime mutex before destroying the JSI runtime

• Worklets: destroy discarded sync call results under the runtime lock

• Worklets: abort pending jobs under the runtime lock on teardown

Other changes

• Worklets: getCurrentThreadId function

• Worklets: pad missing native method arguments with undefined

• worklets: stop AnimationFrameQueue when WorkletsModule is invalidated

• Worklets: stop AnimationFrameQueue dispatch on reentrant invalidate

• Serializable umbrella header for expo

• Worklets: correct RetainingSerializable.h include in umbrella Serializable.h

• Worklets: capture JSX element names into worklet closures

• Worklets: dehoist module.exports assignments

• Worklets: stop workletizing getters, setters and constructors

• Worklets: Crash when handling proto

• builds: too strict lint skip matcher

• add json-ld to the worklets docs

What's Changed

• cherry-pick(worklets-0.12-stable): stop AnimationFrameQueue when WorkletsModule is invalidated

• cherry-pick(worklets-0.12-stable): Crash when handling proto

• cherry-pick(worklets-0.12-stable): release the Synchronizable lock when a setter throws

Key changes

WeakRef on Worklet Runtimes

Worklet Runtimes now support WeakRef. This required enabling Hermes' own microtask queue when the runtime is created, and draining it from C++.

• Worklets: WeakRef on Worklet Runtimes

Bundle Mode script loading on par with React Native

Bundle Mode used to load the script through in-memory copies. On iOS the whole bundle stayed resident in a std::string for the app's lifetime, and on Android a dev-server bundle passed through a Java String and two more copies over JNI. Local bundles are now mmapped and Android dev-server downloads stream to a cache file, the same way React Native's own loaders work. Dev-server fetches now also check the HTTP status and surface the error message Metro returns. In development on Android, initialization reuses the bundle React Native has already downloaded.

• Worklets: bring Bundle Mode script loading on par with React Native

• Worklets: reuse React Native's downloaded dev bundle on Android

enableLocking option in createWorkletRuntime

createWorkletRuntime accepts a new enableLocking option, which creates a Worklet Runtime without mutex guards. It is meant for advanced use cases, where you can guarantee thread-safety of the runtime.

• Worklets: add enableLocking option to createWorkletRuntime

Other changes

• Worklets: Descriptive warning in createSerializable

• Adjust createSerializableInaccessibleObject to the Release createSerializable behavior

• Worklets: RetainingSerializable race condition

• Worklets: web scheduleOnUI implementation on errors

• Worklets: Jest mocks missing APIs

• Worklets: UI loop not pausing when the app is backgrounded

• Worklets: missing autorelease drain on detached worklet threads