I am trying to learn/implement async functions, and I'm unsure why I am not able to get it to work. The 'users' in my async function are coming back undefined. However, the function that makes the database call works just fine.
const getUsers = () => {
const database = firebase.database()
const users = database.ref('users');
users.on('value', function(snapshot) {
const users = []
snapshot.forEach(function(childSnapshot) {
let user = childSnapshot.val();
users.push(user)
});
return users
});
}
async function generateRandomPotentialPartner() {
try {
const users = await getUsers();
console.log(users)
} catch (error) {
console.log(error)
}
}
Use the promise version of on() instead of using the callback version and return that promise from getUsers() function.
Using the callback approach you are currently using, nothing is being returned at all since a return in a callback does not return to the outer function
const getUsers = () => {
const database = firebase.database()
const users = database.ref('users');
// return the on() promise instead of using callback
return users.on('value').then(snapshot => {
const users = []
snapshot.forEach(childSnapshot => {
users.push(childSnapshot.val())
});
return users
});
}
const getUsers = () => {
const database = firebase.database()
const users = database.ref('users');
users.on('value', function(snapshot) {
const users = []
snapshot.forEach(function(childSnapshot) {
let user = childSnapshot.val();
users.push(user)
});
return new Promise((resolve,reject) => {
if(users.length == 0){
reject("There are no users"); //--- Handle rejection
}else {
resolve(users);
}
});
});
}
Your problem is that you are not returning Promises. Asynchronous Javascript is only about promises and chaining.
Related
I have a simple function that checks if the user has Premium access or not:
export const checkPremium = async () =>{
if (auth.currentUser) {
const q = query(collection(db_firestore, 'users'));
onSnapshot(q, (querySnapshot) => {
querySnapshot.forEach((doc) => {
if (doc.id === auth.currentUser.uid) {
return doc.data().userSettings.hasPremium
}
});
})
}
else{
return false
}
}
I tried to catch this in various ways, but no luck, it always returns an "undefined" object.
const getPremium = async => {
checkPremium.then((response) => console.log(response))
}
const getPremium = async => {
let hasPremium = await checkPremium()
}
let hasPremium = checkPremium()
What is the correct way to get the returned Boolean value?
onSnapshot is meant for listening to a collection continuously, getting repeatedly notified as its value changes. It does not create a promise, so the promise returned by getPremium is unrelated to the data you will eventually get in onSnapshot. If you just want to get the value once, you should use getDocs:
export const checkPremium = async () =>{
if (auth.currentUser) {
const q = query(collection(db_firestore, 'users'));
const querySnapshot = await getDocs(q);
const match = querySnapshot.docs.find(doc => doc.id === auth.currentUser.uid);
if (match) {
return doc.data().userSettings.hasPremium);
} else {
return false;
}
}
else{
return false
}
}
Also, instead of getting all the users and then using client side code to find the one with the right id, you could just fetch that individual doc directly:
const ref = doc(db_firestore, 'users', auth.currentUser.uid)
const snapshot = await getDoc(ref);
const data = snapshot.data();
if (data) {
return data.userSettings.hasPremium
} else {
return false
}
The Problem is with the uplines.push.
I always get an empty uplines array so the last part of the code doesn't run. The promises resolve later and I get the correct data. May I know how to go about doing it the correct way?
const getAllUplines = async () => {
uplines = [];
const findUser = async (userFid) => {
const userDoc = await firestore.collection("users").doc(userFid).get();
if (userDoc.exists) {
const user = { ...userDoc.data(), id: userDoc.id };
console.log(user);
uplines.push(user);
if (user.immediateUplineFid) {
findUser(user.immediateUplineFid); //self looping
}
} else {
console.log("No User Found");
return null;
}
};
sale.rens.forEach(async (ren) => {
findUser(ren.userFid);
});
console.log(uplines);
return uplines;
};
let uplines = await getAllUplines();
console.log(uplines);
uplines = uplines.filter(
(v, i) => uplines.findIndex((index) => index === v) === i
); //remove duplicates
uplines.forEach((user) => {
if (user.chatId) {
sendTelegramMessage(user.chatId, saleToDisplay, currentUser.displayName);
console.log("Telegram Message Sent to " + user.displayName);
} else {
console.log(user.displayName + " has no chatId");
}
});
There are a few things that you have missed out while implementing the async call, which are explained in the inline comments in the code snippet.
A short explanation for what happened in your code is that in the line sale.rens.forEach you are passing an async function in the argument, which does not make any difference to the function forEach, it will execute it without waiting for it to complete.
Therefore in my answer I am using Promise.all to wait for all the async function calls to complete before returning the result.
// This is wrapped in an immediately executed async function because await in root is not supported here
(async () => {
const mockGetData = () => new Promise(resolve => setTimeout(resolve, 1000));
const sale = {
rens: [
{ userFid: 1 },
{ userFid: 2 },
{ userFid: 3 }
]
};
const getAllUplines = async () => {
const uplines = [];
const findUser = async (userFid) => {
// Simulating an async function call
const userDoc = await mockGetData();
console.log("User data received");
uplines.push(`User ${userFid}`);
};
const promises = [];
sale.rens.forEach(ren => { // This function in foreach does not have to be declared as async
// The function findUser is an async function, which returns a promise, so we have to keep track of all the promises returned to be used later
promises.push(findUser(ren.userFid));
});
await Promise.all(promises);
return uplines;
};
let uplines = await getAllUplines();
console.log(uplines);
})();
In order to get the results of getAllUplines() properly, you need to add await to all async functions called in getAllUplines().
const getAllUplines = async () => {
uplines = [];
const findUser = async (userFid) => {
const userDoc = await firestore.collection("users").doc(userFid).get();
if (userDoc.exists) {
const user = { ...userDoc.data(), id: userDoc.id };
console.log(user);
uplines.push(user);
if (user.immediateUplineFid) {
await findUser(user.immediateUplineFid); //self looping
}
} else {
console.log("No User Found");
return null;
}
};
sale.rens.forEach(async (ren) => {
await findUser(ren.userFid);
});
console.log(uplines);
return uplines;
};
I am trying to load data from firebase by calling a function in which it filters data and returns them.
When I call this function in my main function, it returns "undefined". I know the data is there (console.log(postsArray)) prints the data but I guess the return executes before data is loaded.
What am I doing wrong?
calling_Function_in_Main = async () => {
const data = await FirebaseData ();
console.log(data);
};
FirebaseData is the function that I call in my main function to load data and to return them
let postsArrays=[];
const FirebaseData = async () => {
const getViewableLink = async (link) => { //some function };
const loadData = async () => {
const database = firebase.database();
const data = database.ref();
const loadProfile = data
.child('Posts')
.orderByChild('Active')
.equalTo(true)
.once('value', function gotData(data) {
Object.values(readInfo).forEach(async (element) => {
element.Option1Link = await getViewableLink(
preLink + element.Option1Link,
);
postsArray.push(element);
}
});
})
.catch((error) => {
console.log(error);
}
})
.then((postsArray) => {
console.log(postsArray);
return postsArray;
});
};
await loadData();
};
export default FirebaseSwipeData;
You can't use foreach with async/await because It is not asynchronous. It is blocking.
you have 2 ways to fix this:
1- Reading in sequence: you can use for...of loop
for(const element of Object.values(readInfo)) {
element.Option1Link = await getViewableLink(
preLink + element.Option1Link,
);
postsArray.push(element);
}
2- Reading in parallel: you can use Promise.all
await Promise.all(Object.values(readInfo).map(async (element) => {
element.Option1Link = await getViewableLink(
preLink + element.Option1Link,
);
postsArray.push(element);
}));
Hope that solves the problem, for you
I am working on a project using react and firebase and redux and I have some items that did created by a user. I'm storing the id of the user in the item object so i can populate the user later when i get the item to display.
Now I'm trying to get the items and modify them by replacing the user id with the actual info about the user but I have a promises problem. In my code I just get an empty array which mean the modification didn't get resolved before I return the final result.
export const getItems = () => {
return (dispatch, getState, { getFirebase }) => {
const firestore = getFirebase().firestore();
const items = [];
const dbRef = firestore.collection('items').orderBy('createdAt', 'desc').limit(2);
return dbRef
.get()
.then((res) => {
const firstVisible = res.docs[0];
const lastVisible = res.docs[res.docs.length - 1];
async function getData(res) {
/////////////////////////////////////////////// how to finish this code befor jumping to the return line
await res.forEach((doc) => {
firestore
.collection('users')
.doc(doc.data().owner)
.get()
.then((res) => {
items.push({ ...doc.data(), owner: res.data() });
});
});
////////////////////////////////////////////////
return { docs: items, lastVisible, firstVisible };
}
return getData(res);
})
.catch((err) => {
console.log(err);
});
};
};
I don't get exactly what you are trying to do, but I would suggest putting some order to make your code easy to read and work with.
You can use for of to manage async looping. I suggest something like this, disclaimer, I did it at the eye, problably there are some errors, but you can get the idea.
const getAllDocs = function (data) {
let temp = [];
data.forEach(function (doc) {
temp.push(doc.data());
});
return { data: temp };
};
const getDoc = snap => (snap.exists ? { data: snap.data() } : {});
export const getItems = () => {
return async (dispatch, getState, { getFirebase }) => {
const firestore = getFirebase().firestore();
const dbRef = firestore.collection('items').orderBy('createdAt', 'desc').limit(2);
const usersRef = firestore.collection('users');
let temps = [];
const { data: items } = await dbRef.get().then(getAllDocs);
const firstVisible = items[0];
const lastVisible = items[items.length - 1];
for (const item of items) {
const { data: user } = await usersRef.doc(item.owner).get().then(getDoc);
const owner = {
/* whatever this means*/
};
temps.push({ ...user, owner });
}
return { docs: temps, lastVisible, firstVisible };
};
};
The problem is that an array of Promises is not itself a Promise -- so awaiting it will be a no-op.
You can solve this using Promise.all if you want to load them all asynchronously.
const items = await Promise.all(res.map(async (doc) => {
const res = await firestore.collection('users').doc(doc.data().owner).get();
return { ...doc.data(), owner: res.data() };
});
Otherwise you can await in a for loop as suggested in other answers.
Now i created an async function getUsers which returns a promise with the correct data. Then, I tried retrieving the data in a form of array by using .then(). However, the data is empty when I call getUsers() in get().
getUsers = async () => {
try {
const users = await AsyncStorage.getItem("#FriendBook:Users");
if (users !== null) {
return JSON.parse(users);
}
return [];
} catch (error) {
console.log("Unable to load users", error);
}
};
get = () => {
var p = getUsers();
var users = [];
p.then((res) => {
users = res;
});
return users;
};