I’ve been out of the loop for a bit but I thought that the Meteor API had promise support with the promise package? I tried adding that (and ecmascript) but .then is undefined. I noticed there are 3rd party packages but i’d rather not depend on monkey patching core.
You should be able to apply an async call back. Here it is in the docs https://docs.meteor.com/api/methods.html
Meteor.call('methodName', params, callback)