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Extracting object returned from promise to push to an array, returning as Promise {<pending>} with [[PromiseValue]] object [duplicate]

My code:
let AuthUser = data => {
return google.login(data.username, data.password).then(token => { return token } )
}
And when i try to run something like this:
let userToken = AuthUser(data)
console.log(userToken)
I'm getting:
Promise { <pending> }
But why?
My main goal is to get token from google.login(data.username, data.password) which returns a promise, into a variable. And only then preform some actions.

The promise will always log pending as long as its results are not resolved yet. You must call .then on the promise to capture the results regardless of the promise state (resolved or still pending):
let AuthUser = function(data) {
return google.login(data.username, data.password).then(token => { return token } )
}
let userToken = AuthUser(data)
console.log(userToken) // Promise { <pending> }
userToken.then(function(result) {
console.log(result) // "Some User token"
})
Why is that?
Promises are forward direction only; You can only resolve them once. The resolved value of a Promise is passed to its .then or .catch methods.
Details
According to the Promises/A+ spec:
The promise resolution procedure is an abstract operation taking as
input a promise and a value, which we denote as [[Resolve]](promise,
x). If x is a thenable, it attempts to make promise adopt the state of
x, under the assumption that x behaves at least somewhat like a
promise. Otherwise, it fulfills promise with the value x.
This treatment of thenables allows promise implementations to
interoperate, as long as they expose a Promises/A+-compliant then
method. It also allows Promises/A+ implementations to “assimilate”
nonconformant implementations with reasonable then methods.
This spec is a little hard to parse, so let's break it down. The rule is:
If the function in the .then handler returns a value, then the Promise resolves with that value. If the handler returns another Promise, then the original Promise resolves with the resolved value of the chained Promise. The next .then handler will always contain the resolved value of the chained promise returned in the preceding .then.
The way it actually works is described below in more detail:
1. The return of the .then function will be the resolved value of the promise.
function initPromise() {
return new Promise(function(res, rej) {
res("initResolve");
})
}
initPromise()
.then(function(result) {
console.log(result); // "initResolve"
return "normalReturn";
})
.then(function(result) {
console.log(result); // "normalReturn"
});
2. If the .then function returns a Promise, then the resolved value of that chained promise is passed to the following .then.
function initPromise() {
return new Promise(function(res, rej) {
res("initResolve");
})
}
initPromise()
.then(function(result) {
console.log(result); // "initResolve"
return new Promise(function(resolve, reject) {
setTimeout(function() {
resolve("secondPromise");
}, 1000)
})
})
.then(function(result) {
console.log(result); // "secondPromise"
});

I know this question was asked 2 years ago, but I run into the same issue and the answer for the problem is since ES2017, that you can simply await the functions return value (as of now, only works in async functions), like:
let AuthUser = function(data) {
return google.login(data.username, data.password)
}
let userToken = await AuthUser(data)
console.log(userToken) // your data

The then method returns a pending promise which can be resolved asynchronously by the return value of a result handler registered in the call to then, or rejected by throwing an error inside the handler called.
So calling AuthUser will not suddenly log the user in synchronously, but returns a promise whose then registered handlers will be called after the login succeeds ( or fails). I would suggest triggering all login processing by a then clause of the login promise. E.G. using named functions to highlight the sequence of flow:
let AuthUser = data => { // just the login promise
return google.login(data.username, data.password);
};
AuthUser(data).then( processLogin).catch(loginFail);
function processLogin( token) {
// do logged in stuff:
// enable, initiate, or do things after login
}
function loginFail( err) {
console.log("login failed: " + err);
}

If that situation happens for a multiple values like an array.
[
Promise { <pending> },
Promise { <pending> },
Promise { <pending> },
Promise { <pending> },
Promise { <pending> }
]
You can use Promise.all() this will resolve all promises.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/all

See the MDN section on Promises. In particular, look at the return type of then().
To log in, the user-agent has to submit a request to the server and wait to receive a response. Since making your application totally stop execution during a request round-trip usually makes for a bad user experience, practically every JS function that logs you in (or performs any other form of server interaction) will use a Promise, or something very much like it, to deliver results asynchronously.
Now, also notice that return statements are always evaluated in the context of the function they appear in. So when you wrote:
let AuthUser = data => {
return google
.login(data.username, data.password)
.then( token => {
return token;
});
};
the statement return token; meant that the anonymous function being passed into then() should return the token, not that the AuthUser function should. What AuthUser returns is the result of calling google.login(username, password).then(callback);, which happens to be a Promise.
Ultimately your callback token => { return token; } does nothing; instead, your input to then() needs to be a function that actually handles the token in some way.

Your Promise is pending, complete it by
userToken.then(function(result){
console.log(result)
})
after your remaining code.
All this code does is that .then() completes your promise & captures the end result in result variable & print result in console.
Keep in mind, you cannot store the result in global variable.
Hope that explanation might help you.

I had the same issue earlier, but my situation was a bit different in the front-end. I'll share my scenario anyway, maybe someone might find it useful.
I had an api call to /api/user/register in the frontend with email, password and username as request body. On submitting the form(register form), a handler function is called which initiates the fetch call to /api/user/register. I used the event.preventDefault() in the beginning line of this handler function, all other lines,like forming the request body as well the fetch call was written after the event.preventDefault(). This returned a pending promise.
But when I put the request body formation code above the event.preventDefault(), it returned the real promise. Like this:
event.preventDefault();
const data = {
'email': email,
'password': password
}
fetch(...)
...
instead of :
const data = {
'email': email,
'password': password
}
event.preventDefault();
fetch(...)
...

Try this
var number1 = document.getElementById("number1");
var number2 = document.getElementById("number2");
startAsync.addEventListener("click", function() {
if (number1.value > 0 && number2.value > 0) {
asyncTest(parseInt(number1.value), parseInt(number2.value)).then(function(result) {
document.getElementById("promiseResolved").textContent = "promiseResolved: " + result
});
} else {
asyncTest(1, 2).then(function(result) {
document.getElementById("promiseResolved").textContent = "promiseResolved: " + result
});
}
});
async function asyncTest(a, b) {
return await (a + b);
};
<button id="startAsync">start Async function</button><br />
<input type="number" id="number1" /><br />
<input type="number" id="number2" /><br />
<span id="promiseResolved"></span><br />

Im my case (JS) I forgot to add await

Node.js Can't fulfill promise (Promise { <pending> })

I m new in asynchronous coding
I m using csvtojson library and I'm trying to convert a csv file and pass the result in an other module .
The convert() function looks like this:
convert: function (csvFilePath) {
return new Promise((resolve, reject) => {
const options = { delimiter: ["|",","],
noHeader: true ,
headers: ["header1", "header2"]
}
csv(options)
.fromFile(csvFilePath)
.on('end_parsed',(convertedJson) => {
resolve(convertedJson);
})
.on("done",(error) => {
reject(error);
})
});
}
My call:
const converter = require ("./converter")();
let json;
json = converter.convert("./importSample.csv");
console.log(json);
When I execute the code I can see that the promise is still on pending state:
Promise { <pending> }
I think that I have to use the .then() function but I don't know where or how.

From converter function you are getting promise, and that object has method then. You should do something like this.
const converter = require ("./converter")();
converter.convert("./importSample.csv").then(json => {
console.log(json);
}).catch(error => {
console.log(error);
});
Here you can find nice tutorial about Promises, and here is documentation for Promises.

Promise has a fixed syntactical architecture. I'll explain it with a simple code.
var x = new Promise((resolve,reject)=>{
//here you perform an asynchronous call
resolve(value); //receive it in 'then' part of promise
reject(error): //if your operation fails due to any error, you call reject, which is handled by 'catch' part of the promise.
});
x.then((value)=>{
//this is the part which was called using resolve, and the value it receives is the value you passed as argument in resolve.
});
x.catch((error)=>{
//this part is called by reject. the error received is the value you passed inside the reject.
});
So, your function should go something like-
converter.convert("./importSample.csv").then((json)=>{
//here is your part of code which is to be handled synchronously after the promise is called.
}).catch((error)=>{
//in case any error occurs and you want your program to exit gracefully.
});

chaining promise (bluebird)

I am using nodeJs and bluebird. i have methode to check for parameters validity, so i create a module where i have (see code below) and all of them are promises.
exports.validateSpeciality = validateSpeciality;
exports.validateGovernorate = validateGovernorate;
exports.validateCities = validateCities;
In my controller (see code below) i always get the first promise result in the then containing "res.send(results)"
validator
.validateSpeciality(speciality)
.then(validator.validateGovernorate(governorate))
.then(validator.validateCities(governorate, cities))
.then(Doctor.searchBySpecialityAndByCities(speciality, cities))
.then(function (results) {
console.log(results);
res.send(results);
})
.catch(function (error) {
console.log(error);
res.status(400).send(error);
})
Can someone explain to me why it is not working in this way? even if one of the promise is rejected it always execute the last then and don't go to catch.

Currently in your Promise chain, you don't use the results of the previous function calls. You run the next promise, when the previous was not resolved. So, even one of the functions: validateGovernorate, validateCities, searchBySpecialityAndByCities rejected with error, the final then will be called anycase.
To fix that, run the next function, when the previous promise is resolved:
validator
.validateSpeciality(speciality)
.then(function() {
return validator.validateGovernorate(governorate);
})
.then(function() {
return validator.validateCities(governorate, cities);
});
.then(function() {
return Doctor.searchBySpecialityAndByCities(speciality, cities);
})
.then(function(results) {
console.log(results);
res.send(results);
})
.catch(function (error) {
console.log(error);
res.status(400).send(error);
});
Also, check that you haven't catch blocks in all the functions: validateGovernorate, validateCities, searchBySpecialityAndByCities. And if you have throw an error there or reject with error.
Check this article there is very good desribed how promises work.

Unit test a function that ends the promise chain

Let's say I have a function in a class named UserController that does something along those lines (where userService.createUser() returns a promise):
function createUser(req, res)
{
const userInfo = req.body;
userService.createUser(userInfo)
.then(function(){res.json({message: "User added successfully"})})
.fail(function(error){res.send(error)})
.done();
}
How can I test that, when the promise resolves, res.json() is called, and when the promise rejects, res.send(error) is called?
I have tried writing a test like this:
const userService = ...
const userController = new UserController(userService);
const response = {send: sinon.stub()};
...
const anError = new Error();
userService.createUser = sinon.stub().returns(Q.reject(anError));
userController.createUser(request, response);
expect(response.send).to.be.calledWith(anError);
But the test fails with "response.send is never called". I also tried logging something before calling res.send(error) and the logging does happen.
My guess is that expect() is called before res.send(error) is executed since it's asynchronous.
I'm fairly new with promises and unit tests, is it something with my architecture or my use of promises?
I'm using Q for promises and mocha, chai, sinon for my unit tests.

As you have an asynchronous call the expect statement is called right after userController.createUser() line. So when the assertion is evaluated it has not been called yet.
To test your code asynchronously you will need to declare done on your it statement and then call it manually to get the result.
On your test file:
it('should work', function(done) {
...
userController.createUser(request, response);
process.nextTick(function(){
expect(response.send).to.be.calledWith(anError);
done();
});
});
This will make Mocha (I'm assuming you are using it) evaluate your excpect just when done() is called.
Alternatively you could set a cb function on your UserController.createUser function and call it on .done():
UserController
function createUser(req, res, cb) {
const userInfo = req.body;
userService.createUser(userInfo)
.then(function(){res.json({message: "User added successfully"})})
.fail(function(error){res.send(error)})
.done(function(){ if(cb) cb() });
}
And then on your test:
userController.createUser(request, response, function() {
expect(response.send).to.be.calledWith(anError);
done();
});

The easier way, assuming you use Mocha or Jasmine as the framework, is to go ahead as you first started, but just skip Sinon completely (as it is not needed here, unless you test for actual arguments received):
// observe the `done` callback - calling it signals success
it('should call send on successful service calls', (done) => {
// assuming same code as in question
...
const response = {send: done};
userController.createUser(request, response);
});
// observe the `done` callback - calling it signals success
it('should call send on failing service calls', (done) => {
// assuming same code as in question
...
const response = {send: err => err? done(): done(new Error("No error received"))};
userController.createUser(request, response);
});
Disclosure: I am part of the Sinon maintainer team.

Chaining Angular promise rejections

I have a chained promise and in the case of a rejection for either of the promises, I need to perform an async operation (get the translated error message). As I've already got a chained promise on success, I assume it's not possible to also chain on rejection - I am attempting to simply nest the async calls, but I'm not getting the resolved promise back from deferred.reject(deferredRejection.promise); below. Pointers appreciated!
login: function(email, password) {
var deferred = $q.defer();
AuthService.login(email, password).then(function(response) {
var user = {
'accountToken': response.accountToken,
'email': response.username,
'onboarded': response.onboarded,
'verified': response.verified
};
return SyncStorageService.write(SyncStorageService.storageKeys.user,
user);
}, function(error) {
// login failed
var deferredRejection = $q.defer();
$translate('ALERTS.LOGIN_FAILED').then(function(translatedValue) {
deferredRejection.resolve(translatedValue);
});
deferred.reject(deferredRejection.promise);
}).then(function(data) {
deferred.resolve(data);
}, function(error) {
// saving data failed
var deferredRejection = $q.defer();
$translate('ALERTS.UNKNOWN').then(function(translatedValue) {
deferredRejection.resolve(translatedValue);
});
deferred.reject(deferredRejection.promise);
});
return deferred.promise;
}
Updated Solution:
Based on the answer below, I was able to re-write the code as follows:
login: function(email, password) {
return AuthService.login(email, password).then(function(response) {
return {
'accountToken': response.accountToken,
'email': response.username,
'onboarded': response.onboarded,
'verified': response.verified
};
}).then(function(data) {
return SyncStorageService.write(SyncStorageService.storageKeys.user,
data);
});
}
Notes:
Both AuthService.login and SyncStorageService.write now reject promises with an Error object (e.g. new Error('ALERT.ERROR_MESSAGE');), which bubbles up through login to the controller (previously was doing the translation at the service level);
The controller that calls the login method has .then() and .catch() blocks - on a .catch(), the passed Error.message is translated and displayed.

It looks like you're not really chaining promises, and using the forgotten promise/deferred anti pattern. Making a few assumptions about how you actually want it to behave, and factoring out the calls to $translate, then something like the following I suspect is what you're after:
login: function(email, password) {
return AuthService.login(email, password).then(function(response) {
return {
'accountToken': response.accountToken,
'email': response.username,
'onboarded': response.onboarded,
'verified': response.verified
};
}, function() {
return $q.reject('ALERTS.LOGIN_FAILED');
}).then(function(user) {
return SyncStorageService.write(SyncStorageService.storageKeys.user, user).catch(function() {
return $q.reject('ALERTS.UNKNOWN');
});
}).catch(function(message) {
return $translate(message).then(function(translatedValue) {
return $q.reject(translatedValue);
});
});
}
The main things to keep in mind are:
If you definitely want to reject the derived promise, return $q.reject(error) from the success or error callback.
All the error callbacks above do this. The ones after attempted login or saving use the translation key as the error that will be eventually passed to the final catch callback. The success callback from $translate also does this to transform its resolved promise to a rejected one, so the final catch callback returns a rejected promise, so the calling code gets a rejected promise, and (presumably) shows the translated error to the user.
If you definitely want to resolve the derived promise, return anything that isn't a promise from he success or error callbacks. The derived promise will be resolved with that value. (This includes undefined if you don't have an explicit return value).
This is what is done above when returning the user return {'accountToken'.... in the first callback.
If you want to defer the resolution/rejection of a promise, return another promise from the success or error callback. Then the derived promise will be eventually resolved or rejected in whatever manner this other promise is resolved/rejected.
This is what's done above when returning SyncStorageService.write..., and when returning $translate(....