SyntaxError exception in React Native Firebase Database

Question

I can't get Firebase realtime database data, getting exception and can't understand why.

"SyntaxError: Unexpected end of input
at App.componentDidMount (blob:http://localhost:8081/debac782-dd29-4750-a1b8-dc8e57c59632:1571:45)
at App.proxiedComponentDidMount (blob:http://localhost:8081/debac782-dd29-4750-a1b8-dc8e57c59632:57980:42)
at commitLifeCycles (blob:http://localhost:8081/debac782-dd29-4750-a1b8-dc8e57c59632:31136:28)
at commitLayoutEffects (blob:http://localhost:8081/debac782-dd29-4750-a1b8-dc8e57c59632:33340:13)
at Object.invokeGuardedCallbackImpl (blob:http://localhost:8081/debac782-dd29-4750-a1b8-dc8e57c59632:20647:16)
at invokeGuardedCallback (blob:http://localhost:8081/debac782-dd29-4750-a1b8-dc8e57c59632:20743:37)
at commitRootImpl (blob:http://localhost:8081/debac782-dd29-4750-a1b8-dc8e57c59632:33172:15)
at unstable_runWithPriority (blob:http://localhost:8081/debac782-dd29-4750-a1b8-dc8e57c59632:55717:18)
at runWithPriority (blob:http://localhost:8081/debac782-dd29-4750-a1b8-dc8e57c59632:24203:16)
at commitRoot (blob:http://localhost:8081/debac782-dd29-4750-a1b8-dc8e57c59632:33041:9)"

In the App.js constructor I initialize firebase like this (works fine):

if (!firebase.apps.length) {
    firebase.initializeApp(config);
}

And in componentDidMount() I am trying to get the database ref:

    componentDidMount() {            
        firebase.database().ref('listings').once("value", snapshot => {
          //handle snapshot data
        });         
   }

No, why? The instruction says nothing about that firebase.googleblog.com/2016/01/… — Dmitri Borohhov
– Dmitri Borohhov, Commented Aug 23, 2019 at 17:31
I am sure but i think ref('lintings').once.....i think mistake is once....instend of once ,there should be on — Kabir
– Kabir, Commented Aug 23, 2019 at 17:37
.on() is for continuous polling, .once() is for a single read. The error is the same. — Dmitri Borohhov
– Dmitri Borohhov, Commented Aug 23, 2019 at 17:40
@DmitriBorohhov I've added my answer. I think you need to make change to reference call. Take care of the syntax. — Yash
– Yash, Commented Aug 23, 2019 at 17:41

Dmitri Borohhov · Accepted Answer · 2019-08-24 15:25:16Z

1

It seems like the remote debugger for React Native is causing syntax errors in bundling. Once I disable remote debugging, the issue disappears and I can get the data from Firebase database.

This looks to be the same as described in the Github issue.

answered Aug 24, 2019 at 15:25

Dmitri Borohhov

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Community · Accepted Answer · 2020-06-20 09:12:55Z

0

Take care of the syntax:

firebase.database().ref('listings').once('value').then(function(snapshot) {
  // handle snapshot data
});

.once() returns a Promise<DataSnapshot> hence, you need to handle it with .then()

once

once(eventType: EventType, successCallback?: function, failureCallbackOrContext?: function | Object | null, context?: Object | null): Promise<DataSnapshot>

From https://firebase.google.com/docs/reference/js/firebase.database.Reference.html#once

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Aug 23, 2019 at 17:40

Yash

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2 Comments

Dmitri Borohhov Over a year ago

Tried your suggestion, didn't work. The syntax is just a lambda expression, which worked fine on a React web project, so I wonder why it doesn't work in a clean React Native project. The second argument of the .once() function is a successCallback, which returns a DataSnapshot when ready.

Dmitri Borohhov Over a year ago

Yes, I did. No change.

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