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Firebase Admin update function calling multiple callbacks in nodejs

I know for a fact that reading data from firebase with firebase admin returns multiple callbacks. that is why I use ref.once(), like example below:
const ref = db.ref('clients');
ref.once('value', (snapshot) => {
res.send(snapshot.val());
}, (errorObject) => {
console.log('The read failed: ' + errorObject.name);
});
But, when I try to update data I get into the same trouble of receiving multiple callbacks crashing my application, but I can't use once in ref.update, what can I do to prevent receiving multiple callbacks?
app.get('/set-client', (req, res) => {
const ref = db.ref(`users/new_users`)
ref.update({ 'client': uid_client}).then(function(){
console.log("Data saved successfully.");
res.status(200).send("successful")
}).catch(function(error) {
console.log("Data could not be saved." + error);
res.status(201).send("failed")
});
});
Here is a code example.

When interacting with responses in the way you've shown, you might find that using the .then(onFulfilled, onRejected) variant of the then() method may be of use.
Quick note: When using this approach, care must be taken to understand that if the onFulfilled handler throws an exception/rejects, the sibling onRejected handler will not be called with its exception. The exception is instead passed onto the next chained onRejected handler in later then/catch calls. The sibling will only catch exceptions/rejections from steps prior to it in the chain.
Here is an example of the difference:
const somePromise = /* ... */;
const resultPromise = somePromise
.then((data) => { /* handle data */ }) // an error thrown here
.catch((err) => { /* handle error */ }) // gets caught here
// vs.
const resultPromise = somePromise
.then(
(data) => { /* handle data */ }, // an error thrown here, will reject resultPromise
(err) => { /* handle error */ } // instead of being handled here
)
This trait of the onRejected handler in .then(onFulfilled, onRejected) can be applied in a way where headers can't be sent twice for the same response. If for whatever reason the onFulfilled handler throws an exception while trying to send a response, the onRejected handler that is also responsible for sending a response is skipped - preventing any headers already sent errors.
This means that the first code block gets swapped out for:
const ref = db.ref('clients');
ref.once('value')
.then(
(snapshot) => { // got data successfully
console.log('got data successfully');
// don't forget to check snapshot.exists() if data could be missing
res.send(snapshot.val()); // using .json() over .send() is recommended for arbitrary data
},
(error) => { // failed to get data/permission
console.error('Failed to read data at /clients: ', error);
res.status(500).send('Data unavailable.');
}
)
.catch(
(error) => { // if here, either of the above blocks failed - probably due to an error related to the response.
console.error('Failed to send response to client: ', error);
try { res.end() } catch (e) {} // forcefully terminate connection if not already
}
);
and the second code block for:
app.get('/set-client', (req, res) => {
const ref = db.ref(`users/new_users`)
ref.update({ 'client': uid_client }) // uid_client is undefined?
.then(
() => {
console.log("Data updated successfully.");
res.status(200).send("successful");
},
(error) => {
console.error("Data could not be saved.", error);
res.status(500).send("failed"); // don't use HTTP 201 Created here
}
)
.catch(
(error) => { // if here, either of the above blocks failed - probably due to an error related to the response.
console.error('Failed to send response to client: ', error);
try { res.end() } catch (e) {} // forcefully terminate connection if not already
}
);
});
The error handler that logs response errors could be rewritten so that it can be reused by taking in the relevant response object (so it can terminated when needed) and returning the error handler:
const buildResponseErrorHandler = (response) => ((error) => {
console.error('Failed to send response to client: ', error);
try { response.end() } catch (e) {} // forcefully terminate connection if not already
});
// usage:
somePromise
.then(
sendResponseHandlerForSuccess,
sendResponseHandlerForFailure
)
.catch(buildResponseErrorHandler(res)) // buildResponseErrorHandler(res) returns (err) => { /* logs problem */ }

How to use single catch function for nested async await?

I have this code:
on('connection', async(socket) => {
try {
const promises = members.map(async(member) => {
try {
const users = await User.find({})
const _promises = users.map(async() => {
try {
//some code here
} catch (err) {
console.log(err)
}
})
await Promise.all(_promises)
} catch (err) {
console.log(err)
}
})
await Promise.all(promises)
} catch (err) {
console.log(err)
throw err
}
})
As you can see I have a try catch for each nested async function. Would it be possible to tweak the code to use only a single catch, or to simplify things somehow?

You can have just a single await at the top level of the handler. If the Promises spawned inside it all chain together to a Promise which is awaited at the top level (like in your example), that top await will catch errors thrown anywhere inside.
But, your catch section should not throw another error unless .on handles Promise rejections as well, otherwise you'll get an unhandled Promise rejection:
on('connection', async(socket) => {
try {
const promises = members.map(async(member) => {
const users = await User.find({})
const _promises = users.map(async() => {
//some code here which may throw
});
await Promise.all(_promises);
});
await Promise.all(promises);
} catch (err) {
console.log(err);
}
})
If await User.find throws, then the promises array will contain a Promise which rejects, which mean that the top await Promise.all(promises); will throw and be caught
If something inside users.map throws, _promises will contain a Promise which rejects, so await Promise.all(_promises); will throw. But that's inside the const promises = members.map callback, so that will result in promises containing a rejected Promise too - so it will be caught by the await Promise.all(promises); as well.

If a function you call throws an error, the error will fall back to the nearest catch block the function call is enclosed in.
try {
throw "an error";
}
catch(e) {
console.log(e); //output: "an error"
}
Now consider this
try {
try {
throw "an error";
}
catch(e) {
console.log(e); //output: "an error"
}
}
catch(e) {
console.log(e); //This line is not going to be executed
}
This mechanism enables attachment of more error information to the generated error in each level. Imagine your error is an object and each nested catch bock attaching its own information to the error object an pass it along by throwing again.
Look at the following code:
try {
try {
throw {internalError: 101};
}
catch(e) {
//Attach more info and throw again
e.additionalInfo = 'Disconnected when gathering information';
throw e;
}
}
catch(e) {
e.message = 'Cannot get information'
console.log(e); //Final error with lot of information
}

How to properly handle error in MongoDB bulkwrite? [duplicate]

I like the flatness of the new Async/Await feature available in Typescript, etc. However, I'm not sure I like the fact that I have to declare the variable I'm awaiting on the outside of a try...catch block in order to use it later. Like so:
let createdUser
try {
createdUser = await this.User.create(userInfo)
} catch (error) {
console.error(error)
}
console.log(createdUser)
// business
// logic
// goes
// here
Please correct me if I'm wrong, but it seems to be best practice not to place multiple lines of business logic in the try body, so I'm left only with the alternative of declaring createdUser outside the block, assigning it in the block, and then using it after.
What is best practice in this instance?

It seems to be best practice not to place multiple lines of business logic in the try body
Actually I'd say it is. You usually want to catch all exceptions from working with the value:
try {
const createdUser = await this.User.create(userInfo);
console.log(createdUser)
// business logic goes here
} catch (error) {
console.error(error) // from creation or business logic
}
If you want to catch and handle errors only from the promise, you have three choices:
Declare the variable outside, and branch depending on whether there was an exception or not. That can take various forms, like
assign a default value to the variable in the catch block
return early or re-throw an exception from the catch block
set a flag whether the catch block caught an exception, and test for it in an if condition
test for the value of the variable to have been assigned
let createdUser; // or use `var` inside the block
try {
createdUser = await this.User.create(userInfo);
} catch (error) {
console.error(error) // from creation
}
if (createdUser) { // user was successfully created
console.log(createdUser)
// business logic goes here
}
Test the caught exception for its type, and handle or rethrow it based on that.
try {
const createdUser = await this.User.create(userInfo);
// user was successfully created
console.log(createdUser)
// business logic goes here
} catch (error) {
if (error instanceof CreationError) {
console.error(error) // from creation
} else {
throw error;
}
}
Unfortunately, standard JavaScript (still) doesn't have syntax support for conditional exceptions.
If your method doesn't return promises that are rejected with specific enough errors, you can do that yourself by re-throwing something more appropriate in a .catch() handler:
try {
const createdUser = await this.User.create(userInfo).catch(err => {
throw new CreationError(err.message, {code: "USER_CREATE"});
});
…
} …
See also Handling multiple catches in promise chain for the pre-async/await version of this.
Use then with two callbacks instead of try/catch. This really is the least ugly way and my personal recommendation also for its simplicity and correctness, not relying on tagged errors or looks of the result value to distinguish between fulfillment and rejection of the promise:
await this.User.create(userInfo).then(createdUser => {
// user was successfully created
console.log(createdUser)
// business logic goes here
}, error => {
console.error(error) // from creation
});
Of course it comes with the drawback of introducing callback functions, meaning you cannot as easily break/continue loops or do early returns from the outer function.

Another simpler approach is to append .catch to the promise function. ex:
const createdUser = await this.User.create(userInfo).catch( error => {
// handle error
})

Cleaner code
using async/await with Promise catch handler.
From what I see, this has been a long-standing problem that has bugged (both meanings) many programmers and their code. The Promise .catch is really no different from try/catch.
Working harmoniously with await/async, ES6 Promise's catch handler provides a proper solution and make code cleaner:
const createUser = await this.User
.create(userInfo)
.catch(error => console.error(error))
console.log(createdUser)
// business
// logic
// goes
// here
Note that while this answers the question, it gobbles up the error. The intention must be for the execution to continue and not throw. In this case, it's usually always better to be explicit and return false from catch and check for user:
.catch(error => {
console.error(error);
return false
})
if (!createdUser) // stop operation
In this case, it is better to throw because (1) this operation (creating a user) is not expected to failed, and (2) you are likely not able to continue:
const createUser = await this.User
.create(userInfo)
.catch(error => {
// do what you need with the error
console.error(error)
// maybe send to Datadog or Sentry
// don't gobble up the error
throw error
})
console.log(createdUser)
// business
// logic
// goes
// here
Learning catch doesn't seem like worth it?
The cleanliness benefits may not be apparent above, but it adds up in real-world complex async operations.
As an illustration, besides creating user (this.User.create), we can push notification (this.pushNotification) and send email (this.sendEmail).
this.User.create
this.User.create = async(userInfo) => {
// collect some fb data and do some background check in parallel
const facebookDetails = await retrieveFacebookAsync(userInfo.email)
.catch(error => {
// we can do some special error handling
// and throw back the error
})
const backgroundCheck = await backgroundCheckAsync(userInfo.passportID)
if (backgroundCheck.pass !== true) throw Error('Background check failed')
// now we can insert everything
const createdUser = await Database.insert({ ...userInfo, ...facebookDetails })
return createdUser
}
this.pushNotifcation and this.sendEmail
this.pushNotification = async(userInfo) => {
const pushed = await PushNotificationProvider.send(userInfo)
return pushed
})
this.sendEmail = async(userInfo) => {
const sent = await mail({ to: userInfo.email, message: 'Welcome' })
return sent
})
Compose the operations:
const createdUser = await this.User
.create(userInfo)
.catch(error => {
// handle error
})
// business logic here
return await Promise.all([
this.pushNotification(userInfo),
this.sendEmail(userInfo)
]).catch(error => {
// handle errors caused
// by pushNotification or sendEmail
})
No try/catch. And it's clear what errors you are handling.

I usually use the Promise's catch() function to return an object with an error property on failure.
For example, in your case i'd do:
const createdUser = await this.User.create(userInfo)
.catch(error => { error }); // <--- the added catch
if (Object(createdUser).error) {
console.error(error)
}
If you don't like to keep adding the catch() calls, you can add a helper function to the Function's prototype:
Function.prototype.withCatcher = function withCatcher() {
const result = this.apply(this, arguments);
if (!Object(result).catch) {
throw `${this.name}() must return a Promise when using withCatcher()`;
}
return result.catch(error => ({ error }));
};
And now you'll be able to do:
const createdUser = await this.User.create.withCatcher(userInfo);
if (Object(createdUser).error) {
console.error(createdUser.error);
}
EDIT 03/2020
You can also add a default "catch to an error object" function to the Promise object like so:
Promise.prototype.catchToObj = function catchToObj() {
return this.catch(error => ({ error }));
};
And then use it as follows:
const createdUser = await this.User.create(userInfo).catchToObj();
if (createdUser && createdUser.error) {
console.error(createdUser.error);
}

#Bergi Answer is good, but I think it's not the best way because you have to go back to the old then() method, so i think a better way is to catch the error in the async function
async function someAsyncFunction(){
const createdUser = await this.User.create(userInfo);
console.log(createdUser)
}
someAsyncFunction().catch(console.log);
But what if we have many await in the same function and need to catch every error?
You may declare the to() function
function to(promise) {
return promise.then(data => {
return [null, data];
})
.catch(err => [err]);
}
And then
async function someAsyncFunction(){
let err, createdUser, anotherUser;
[err, createdUser] = await to(this.User.create(userInfo));
if (err) console.log(`Error is ${err}`);
else console.log(`createdUser is ${createdUser}`);
[err, anotherUser] = await to(this.User.create(anotherUserInfo));
if (err) console.log(`Error is ${err}`);
else console.log(`anotherUser is ${anotherUser}`);
}
someAsyncFunction();
When reading this its: "Wait to this.User.create".
Finally you can create the module "to.js" or simply use the await-to-js module.
You can get more information about to function in this post

await this.User.create(userInfo).then(async data => await this.emailService.sendEmail(data.email), async error => await this.sentryService.sendReport(error))

How to send value from Promise 'then' to 'catch'?

I just want to ask how should I pass the resolve promise to catch if the value on the resolve is not intended.
e.g.
let prom = getPromise();
prom.then(value => {
if (value.notIWant) {
// Send to catch <-- my question is here, I want to pass it on the catch.
}
// Process data.
}).catch(err => {
// Pass the error through ipc using json, for logging.
});
I tried to using throw but the object cant be parsed to json and just got an empty object.
ANSWER:
#BohdanKhodakivskyi first comment below is the answer I want.
#31py answer is also correct but the #BohdanKhodakivskyi solution is much simplier and will render the same result.

Simply use throw value;. In your case:
prom.then(value => {
if (value.notIWant) {
// Send to catch
throw value;
}
// Process data.
}).catch(err => {
// Pass the error through ipc using json, for logging.
});
Please also note the difference and limitations between using Promise.reject() and throw which is perfectly described in this question. For example, throw will not work in some async scenarios.

You can simply return a rejected promise:
prom.then(value => {
if (value.notIWant) {
return Promise.reject('your custom error or object');
}
// Process data.
}).catch(err => {
console.log(err); // prints 'your custom error or object'
});
.catch actually handles any promise rejection in the chain, so if you're returning a rejected promise, the control automatically flows to catch.

why you just not rethrow the error? throw new Error("something");

You can use outside functions to do it:
var processData = function(data) {
// process data here
}
var logIt = function(data) {
// do logging here..
}
let prom = getPromise();
prom.then(value => {
if (value.notIWant) {
// Send to catch <-- my question is here, I want to pass it on the catch.
logIt(/*pass any thing*/);
}
// Process data.
processData(data);
}).catch(err => {
logIt(/*pass any thing*/);
});

Error : Callback was already called when using pg-promise with async series

I'm having trouble understanding the output printed why executing this code :
1
2
Unhandled rejection Error: Callback was already called.
It seems like both then and catch are executed when the query is successful.
Any idea ?
Cheers
async.series([
function(callback) {
db.none(query)
.then(function () {
return callback(null, true);
})
.catch(function (err) {
return callback(err, null);
});
},
function(callback) {
db.any(query)
.then(function (data) {
console.log('1')
return callback(null, data);
})
.catch(function (err) {
console.log('2')
console.log(err);
return callback(err, null);
});
}
],
function(err, results) {
if (results && !results[1].isEmpty()) {
// do something
}
});
EDIT :
TypeError: results[1].isEmpty is not a function
It seems like the problem come from the rest of the code and was just a simple undefined function error, thanks.
But i still don't understand something : why is this error catched inside the second query instead of outside the async queries ?

I'm the author of pg-promise.
You should never use async library with pg-promise, it goes against the concept of shared/reusable connections.
Implementation with proper use of the same connection, via a task:
db.task(t => {
return t.batch([
t.none(query1),
t.any(query2)
]);
})
.then(data => {
// data[0] = null - result of the first query
// data[1] = [rows...] - result of the second query
callback(null, data); // this will work, but ill-advised
})
.catch(error => {
callback(error, null); // this will work, but ill-advised
});
See also: Chaining Queries.
However, in your case it looks like when you call the successful callback(null, data), it throws an error, which in turn results in it being caught in the following .catch section. To test this, you can change your promise handler like this:
.then(data => {
callback(null, data);
}, error => {
callback(error, null);
});
It should normally throw an error about Promise missing .catch because you threw an error while in .then and there is no corresponding .catch chained below, which you can also check through this code:
.then(data => {
callback(null, data);
}, error => {
callback(error, null);
})
.catch(error => {
// if we are here, it means our callback(null, data) threw an error
});
P.S. You really should learn to use promises properly, and avoid any callbacks altogether. I only provided an example consistent with your own, but in general, converting promises into callbacks is a very bad coding technique.

This is what happens:
callback(null, data) is called within the context of the .then();
async notices that this was the last item of the series, so it calls the final handler (still within the context of the .then());
the final handler throws an error;
because the code runs in the context of .then(), the promise implementation catches the error and calls the .catch();
this calls the callback again;
PoC:
const async = require('async');
async.series([
callback => {
Promise.resolve().then(() => {
callback(null);
}).catch(e => {
callback(e);
});
}
], err => {
throw Error();
})

Have you try to define your function externally:
function onYourFunction() {
console.log('Hi function');
}
and than do:
.then(onYourFunction) //-->(onYourFunction without parentheses )
Unfortunately i don't use pg-promise but i can advise promise
at this point i create all promises that are necessary:
function createPromise(currObj) {
return new Promise(function (resolve, reject) {
currObj.save(function (errSaving, savedObj) {
if(errSaving){
console.log("reject!");
return reject(errSaving, response);
}
console.log('currObj:' + currObj);
return resolve(savedObj);
});
});
}
and then in cascades:
var allPromiseOs = Promise.all(promise1, promise2, promise3);