Returning objects from Worklet Functions?

[alexphl]

Heyo, I'm migrating from react-native-worklets-core to react-native-worklets and I am blocked by the fact that there's seemingly no way to return anything from an async worklet.

My pain point is this

const runtime = createWorkletRuntime();

// Create Worklet Function once
const worklet = runOnRuntime(runtime, (data: object) => {
  "worklet";
  const res = doSomeWork(data); // also a worklet, duh
  console.log(res); // res logs as expected
  return res;
});
  
 // Call from JS and use the returned value
const returned = await worklet(someData);
console.log(res) // => undefined 😡

As I understand, the only way to accomplish returning data to JS currently is to pass a callback function that would assign to a pre-existing object on the JS runtime. Then I would need to use some message passing pattern to know when the worklet has returned. Not very ergonomic.

Am I missing anything? I see that runOnRuntimeAsync has been outlined in API discussions and is basically what I need here, but as it has not been implemented yet, what is the best migration solution at the moment?

[tjzel]

Hi @alexphl, as you mentioned, runOnRuntimeAsync is not yet implemented.

If you want to return a value with a promise, the best approach at the moment is to manually make a promise, i.e.:

import {
  createWorkletRuntime,
  scheduleOnRuntime,
  scheduleOnRN,
} from 'react-native-worklets';

const workletRuntime = createWorkletRuntime({ name: 'MyRuntime' });

const promise = new Promise<string>((resolve) => {
  scheduleOnRuntime(workletRuntime, () => {
    'worklet';
    console.log('Resolving promise on worklet runtime');
    scheduleOnRN(resolve, 'Promise resolved on worklet runtime');
  });
});

promise
  .then((message) => {
    console.log(message);
  })
  .catch(() => {});