React Native: How to export a method with a return value?

Question

What is the best way to export a method with a return value in React Native?

I know there is RCT_EXPORT_METHOD, but that only works for methods that are

Answer 1

Try return values with Callbacks

RCT_EXPORT_METHOD(findEvents:(RCTResponseSenderBlock)callback)
{
  NSArray *events = ...
  callback(@[[NSNull null], events]);
}

Answer 2

You can also now use promises, which tend to look a little nicer in your JS.

Objective C:

RCT_REMAP_METHOD(getThing, resolver: (RCTPromiseResolveBlock)resolve
     rejecter:(RCTPromiseRejectBlock)reject)
{
  if( condition ) {
    NSString *thingToReturn = @"ALL OK";
    resolve(thingToReturn);
  } else {
    reject([NSError errorWithDomain:@"com.companyname.app" code:0 userInfo:@{ @"text": @"something happend" }]);
  }
}

Then in JS:

async onPress() {
  try {
    const status = await CustomModule.getThing();
    // do something with status
  } catch(e) {
    console.error(e);
  }
}

Answer 3

Seems no way yet. That should be a feature to support.