Promise from jslib to c#

I have an issue getting data from my Firebase database. I've written a jslib which can read and write data in the database. My issue is that the function to read from the database doesn't return anything. I'm pretty sure this is caused by JavaScript being asynchronous, so it wont wait for the database to answer, therefore it just returns the promise of getting the value, instead of the actual value. What I think I need help with is either: A way to interpret the promise in C# A way to return the actual value instead of the promise