running queries in firebase using async / await

Question

Appreciating that firebase has added support for promises, is there a way to run a query like the following inside of an async function?:

const eventref = this.db.ref('cats/whiskers');
const value = await eventref.once('value')

Running the above returns a promise for value, I'm hoping to get the json blob that is stored at cats/whiskers.

Brewer

Yes, why wouldn't it be possible? Have you tried it? Do you have a problem? – Apostrophe

As mentioned, the above returns a promise and not a value. – Brewer

Hm, that should not be possible, await cannot return thenables. Do you use a transpiler? Have you inspected what the eventref.once('value') looks like in a debugger? – Apostrophe

Works for me: runkit.com/5906914d3ff14f0012d0307e/590691ab301f4d0012938bc5 – Counterpart

yeah, for some reason I was sticking the .val() call in the await statement, this worked for me, too. – Brewer

.once works but .on (so someRef.on('child_added')) expects a second argument. Any ideas for that? – Turro

.on don't return a Promise. – Mcdowell

Answer 1

The result of value is a snapshot, we need 1 more step to get the value. This should be like:

const eventref = this.db.ref('cats/whiskers');
const snapshot = await eventref.once('value');
const value = snapshot.val();

Bevin

Totally saved me! – Prolepsis

What if you need to use the value afterwards, will this tell your code to wait for value to be assigned something before proceeding? – Zircon

@Zircon for your reference firebase.google.com/docs/reference/js/… – Bevin

@Zircon value event can be used to retrieve the current value of a specific node in your database using once or can be used to subscribe to changes on a specific node in your database using on. – Bevin

What I mean is. Let's say I need to retrieve the snapshot and store it inside of var A... then I have a code that takes var A and displays it. Is there a way to tell my code to wait until the snapshot is finished retrieving so that var A wont be undefined? I do know you can use .then but sometimes that makes the code very messy. Especially if var A isn't used until much later in the code. – Zircon

@Zircon you can just use await: var A = await eventref.once('value'); because what you're talking about is exactly what await do. – Bevin

Thank you. Will it still continue processing code that doesn't require var A in this example? – Zircon

@ShajeelAfzal just wrap the block in try-catch – Bevin