why is my variable elecfirebase always equal to [ ]?

Question

I have i do a request, after this my variable (elecfirebase) is always [ ]

function a(){
let elecfirebase=[]
    firebase
        .database()
        .ref("/fournisseurs")
        .child(0)
        .child("data")
        .on("value", data => {
          elecfirebase=data.val();    
      });
console.log("elecfirebase ",elecfirebase)
}

can you move `console.log("elecfirebase ",elecfirebase)` inside `.on("value", data => { elecfirebase=data.val(); console.log("elecfirebase ",elecfirebase) });` — Sourabh Somani, Jan 29 '20 at 03:17
when i move `console.log("elecfirebase ",elecfirebase) });` inside, i have the good output — loveALgo, Jan 29 '20 at 03:20
Yeah but you have `console.log` outside and firebase function is async it will fire after getting data — Sourabh Somani, Jan 29 '20 at 03:20

Sourabh Somani · Accepted Answer · 2020-01-29T03:31:40.083

2

console.log("elecfirebase ",elecfirebase) Above console.log will always give you [] because firebase function is async function

You can call a function after getting the data like as follows

function a(){
    let elecfirebase=[]
    firebase
        .database()
        .ref("/fournisseurs")
        .child(0)
        .child("data")
        .on("value", data => {
          elecfirebase=data.val(); 
          onData(elecfirebase);
      });

}
function onData(elecfirebase){
     console.log(elecfirebase)
}

If you want to use this value somewhere else too then use callback or promise. Here is the example of callback

function foo(){
...
...
//calling function with callback
a(function(elecfirebase){

})
...
...
}

function a(callback){
    let elecfirebase=[]
    firebase
        .database()
        .ref("/fournisseurs")
        .child(0)
        .child("data")
        .on("value", data => {
          elecfirebase=data.val(); 
          callback(elecfirebase);
      });

}

Hope it will be helpful

edited Jan 29 '20 at 03:31

answered Jan 29 '20 at 03:24

Sourabh Somani

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Thx for this answers! – loveALgo Jan 29 '20 at 03:26
But here , i want to return elecfirebase from a(); i put console.log() to verify the output – loveALgo Jan 29 '20 at 03:27
Then you need to use callback because this is async method – Sourabh Somani Jan 29 '20 at 03:29
I have added example of the callback – Sourabh Somani Jan 29 '20 at 03:31
is it possible to do `let value= a(function(elecfirebase){ return elecfirebase})` ? – loveALgo Jan 29 '20 at 04:09
1

So value will get the array that a(...) will return – loveALgo Jan 29 '20 at 04:10

why is my variable elecfirebase always equal to [ ]?

1 Answers1