Firebase Handle Async Function

Question

I have a firebase function that goes as follows:

exports.myFunction = functions.database.ref('/users/{id}/').onWrite((snapshot, context) => {

//do some processing here

var number;
snapshot.after.ref.parent.once('value').then((newSnapshot) => {
    number = newSnapshot.child('number').val();
});
console.log(number);

//do some processing with the use of var number

//returning the updates after processing
return snapshot.after.ref.update(updates);
});

I realized that the variable number is coming out to be undefined as the function that I am using to obtain the value of number is running asynchronously. However, I am unable to think of a method to convert this implementation so that it works the way I want it. Any help would be appreciated.

LundinCast · Accepted Answer · 2018-07-04 09:49:31Z

2

You can chain a new .then() to perform the processing on this number. For example:

exports.myFunction = functions.database.ref('/users/{id}/').onWrite((snapshot, context) => {

...
var number;
return snapshot.after.ref.parent.once('value').then((newSnapshot) => {
        number = newSnapshot.child('number').val();
    }).then((number) => {
        console.log(number);
        //do some processing with the use of var number
        snapshot.after.ref.update(updates);
    });
});

edited Jul 4, 2018 at 9:49

answered Jul 4, 2018 at 8:38

LundinCast

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3 Comments

Alex Over a year ago

It should work just like this, or am I wrong ? :

snapshot.after.ref.parent.once('value').then(newSnapshot => {     number = newSnapshot.child('number').val();     console.log(number);     //do some processing with the use of var number });

speedster01 Over a year ago

How do I handle the last return statement in these cases? The updates that are returned are dependent on the processing done with var number.

LundinCast Over a year ago

You can return the whole chain. See my updated answer.

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