CODEWITHSUNDEEP
javascriptpromiseasync-await
gp04lch
gp04lch

Reputation: 1

Await returns [Function] instead of value

await returns [Function] instead of value

Trying to return the values of a query from firebase by making use of the async and await function. Results returned are either [Function] or Unhandled Promise Rejection Warnings. New to promises, async and await but I've tried the basic examples on a few websites, most having the resolve and reject parameters, which I assume should be the same as the firebase promises.

I tried 2 different version, both with incorrect results. 

get_all_users:async function(){
   ref = db.ref("/user_data");
   const value = await ref.orderByKey().on("child_added", function(data){});
   console.log(value.val().name);
}

returns UnhandledPromiseRejectionWarning

function get_async_users(){
  ref = db.ref("/user_data");
  ref.orderByKey().on("child_added", function(data) {
    return data.val().name;
  });
}

returns undefined

Expected either one to return the names from the query.

Upvotes: 0

Views: 80

Answers (1)

Jonas Wilms
Jonas Wilms

Reputation: 138257

on is for listening to all events that ever get triggered. Therefore it does not return a Promise, as a Promise represents a single value being available, and as it does not return a Promise, you can't await it (or at least: it doesn't make sense to do so, its a no-op).

If you want to wait for the first occurence, there is once, which also returns a promise that can be awaited.

Concerning the UnhandledPromiseRejection: You should always wrap your asynchronous code into a try / catch (inside an async function), or attach a .catch to the upmost promise in the chain, then you can handle those errors correctly.

Upvotes: 1

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