[🐛] Poor error message when setBackgroundMessageHandler is not async

[ToyboxZach]

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Issue

I was getting a "TypeError: Cannot read property 'then' of undefined, js engine: hermes" on android

and could not figure out what was causing it

function onBackgroundNoticiation(){
}
messaging().setBackgroundMessageHandler(onBackgroundNoticiation);

Just discoverd that setBackgroundMessageHandler expects an async function so resolving that

async function onBackgroundNoticiation(){
}
messaging().setBackgroundMessageHandler(onBackgroundNoticiation);

Gets rid of that problem

---

Javascript

Click To Expand

package.json:

    "@react-native-firebase/app": "^14.11.1",
    "@react-native-firebase/crashlytics": "^14.11.1",
    "@react-native-firebase/messaging": "^14.11.1",

firebase.json for react-native-firebase v6:

# N/A

iOS

N/A

Android

Click To Expand

Have you converted to AndroidX?

• [x ] my application is an AndroidX application?
• [ ] I am using android/gradle.settings jetifier=true for Android compatibility?
• [ ] I am using the NPM package jetifier for react-native compatibility?

android/build.gradle:

// N/A

android/app/build.gradle:

// N/A

android/settings.gradle:

// N/A

MainApplication.java:

// N/A

AndroidManifest.xml:

<!-- N/A -->

---

Environment

Click To Expand

RN: 0.69.1

• Platform that you're experiencing the issue on:
  • [ ] iOS
  • [ x] Android
  • [ ] iOS but have not tested behavior on Android
  • [ ] Android but have not tested behavior on iOS
  • [ ] Both
• react-native-firebase version you're using that has this issue:
  • 14.11.1
• Firebase module(s) you're using that has the issue:
  • messaging
• Are you using TypeScript?
  • N

---

• 👉 Check out React Native Firebase and Invertase on Twitter for updates on the library.

[mikehardy]

Hi there! How do you propose to solve the issue? In my experience this is what typescript is for, really. You would receive a type error for attempting to send in a function with the wrong signature. We publish typescript types. What would you propose ?

[ToyboxZach]

Maybe be able to catch the error and give a reasonable error message?

I'm not sure how hard that would be, when I looked deeper in the docs it was easy to tell the issue, but I had the error randomly returning for months and could not figure out because it was not descriptive.

It also seems non-intuitive that this would cause a crash in the first place, I don't see why it has to be asynchronous especially since its not returning anything anyways.

[mikehardy]

android headless mode has a number of eccentricities and I assume (though do not know for certain, sorry) that it is related to them

I was thinking more about examining available methods on the Object prototype to see if then was a method, that is, reflectively inspect the passed in object.

That way you've got fail fast (when the method is called, so you see it in development) instead of fail-late where you get a crash and have to pick up the pieces

Something like this https://stackoverflow.com/questions/38508420/how-to-know-if-a-function-is-async

[ToyboxZach]

I just took a look at the code and I see that it is just getting passed back in to react native.

I do believe this would resolve the problem completely

AppRegistry.registerHeadlessTask("ReactNativeFirebaseMessagingHeadlessTask", () => {
  if (!backgroundMessageHandler) {
    // eslint-disable-next-line no-console
    console.warn(
      'No background message handler has been set. Set a handler via the "setBackgroundMessageHandler" method.'
    );
    return () => Promise.resolve();
  }
  return async (remoteMessage) => {
    return await backgroundMessageHandler(remoteMessage);
  };
});

But not sure if that is good standards are anything.

I do see it is my fault for just ignoring the types on this module out of laziness, so I could be fine with a no-fix here, and hopefully just the existence of this bug will help other people who are running into a similar problem.

[Mbiakop1]

I think you are getting that error because the DataModel.getList() doesn't return a Promise so you can have access to Promise then chain. All you have to do is to add a return keyword in the getList before the fetch function so the getList method can return a resolve Promise instead of undefined

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