无法从Firebase函数中获取setState

Question

first i set listaa as a global variable
i'm trying to take out the variable(array) "listaa" from the firebase function that sets it... I'm plannig to use it later to make some maths. I used console.log(listaa) inside the firebase function and it worked, but then when i try to use it() outside(the firebase function) it doens't work. I tried to use setState to make it usable outside but didnt work too

if (funcionar == 0) {
        //============================================================== ANTES ===================================================
        var newRef = firebase
          .database()
          .ref()
          .child("TransferenciasPraVendedores/")
          .push({
            vendedor: vend,
            dia: functions.dataHoje(),
            hora: functions.horaHoje()
          });


        var fire = database.ref("EstoqueCadaVendedor/" + vend);
        fire.once("value", snap => {
          items = [];
          snap.forEach(data => {
            items.push({
              key: data.key,
              data: data.val()
            });
          });
          console.log("items:");
          console.log(items);

          for (j = 0; j < prod.length; j++) {
            // var a = parseInt(snap.val().quantidade);
            console.log("d: " + items[j].data);
            listaa.push(items[j].data);
          }
          // this.setState({ lista:listaa })
          // console.log("lista:");
          // console.log(this.state.lista[2]);
          console.log("listaa");
          console.log(listaa);
        });
        console.log("listaaaaaaaaaaaaaa");
        console.log(listaa);

Ill use 'listaa' here:

        for (i = 0; i < prod.length; i++) {
          firebase
            .database()
            .ref()
            .child("EstoqueCadaVendedor/" + vend + "/")
            .update({
              [prod[i].key]: parseInt(quantNova[i]) + listaa[i]
            });
        }

        // this.setState({ quantidade: [], vendedor: "" });
      }

Answer 1

Did you review the order of the log messages ? if you look carefully, you will recognize the data gets available after later in the process. You probably need to use async/promise to wait until the data gets available or you can use a call back function

async

function to make sure the data is available in the list before you use it.

An async function can contain an await expression, that pauses the execution of the function and waits for the passed Promise's resolution, and then resumes the async function's execution and returns the resolved value.

In the example below, I am passing a call back function that gets called when data is available :

  export function listReleases(callback) {
  //console.log("hello from list releases ");
  releasesRef.once("value").then(
    function(snapshot) {
      const releases = snapshot.val();
      if (releases) {
        callback("releases", releases);
      }
    },
    function(error) {
      // The Promise was rejected.
      console.error(error);
    }
  );
}

+++++++++++++++++++++++++++


 //call the function to get the data and pass a call back function 
 releases = listReleases(this.myCallback);


 myCallback = (key, value) => {
   //do whatever you need to do in here 
 };

Answer 2

Tuan over here.

• The reason why you don't see it is because your code is asynchronous, so when you print console.log() at the end. The firebase calls haven't finished yet.This is a typical race condition scenario.

• FYI, I personally prefer to use the promise style rathen than the callback, I think it makes the code cleaner and easier to read. Try this:

  let firebaseDB = firebase.database();

  if (funcionar == 0) {

   return firebaseDB.ref("TransferenciasPraVendedores/") .push({ vendedor: vend, dia: functions.dataHoje(), hora: functions.horaHoje() }) .then(() => { return firebaseDB.ref("EstoqueCadaVendedor/" + vend).once('value'); .then(snapshot => { let snap = snapshot.val(); items = []; snap.forEach(data => { items.push({ key: data.key, data: data.val() }); }); return {snap, items}; }) .then({snap, items} => { for (j = 0; j < prod.length; j++) { listaa.push(items[j].data); } //console.log(lista)// NOW your lista should have all the items // I would dispatch your redux action here. }) .catch(error => { throw error } 

Let me know if it helped. I can look into it more in depth. Saludos :)