Polyfills

The react-native-webworker library includes built-in polyfills to provide essential web APIs that are missing from Hermes. Every worker automatically gets these polyfills loaded before your code runs.

Why are polyfills needed?

Hermes is a lightweight JavaScript engine optimized for React Native, but it doesn’t implement all the standard Web APIs that you might expect in a browser environment (like Chrome’s V8 or Safari’s JavaScriptCore).

To ensure that standard libraries and isomorphic code work correctly, react-native-webworker injects a set of polyfills into the worker environment.

Included polyfills

Currently, the following APIs are polyfilled:

• AbortController: Allows you to abort asynchronous operations (like fetch requests).
• TextEncoder / TextDecoder: For encoding and decoding strings to/from binary data.

(More polyfills will be added in future versions)

Adding new polyfills

If you are contributing to the library, you can extend the polyfill bundle by adding new APIs:

1. Install the polyfill package in packages/polyfills:

   cd packages/polyfills
   yarn add text-encoding-polyfill

2. Import it in the source file:

   packages/polyfills/src/index.js

   import 'abort-controller/polyfill';
   import 'text-encoding-polyfill';  // New polyfill

3. Rebuild the polyfills:

   cd packages/polyfills
   yarn build

The new polyfill will be automatically available in all workers.