Develop Reference

how can i get value out of a child function [duplicate]

This question already has answers here:
How do I return the response from an asynchronous call?
(41 answers)
Closed 2 years ago.
var checkAcount = (usr, pass) => {
var sql = "SELECT * FROM account WHERE userName = '" +usr+"'" ;
con.query(sql, (err, result) => {
if(err) throw err;
if(result.length > 0){
bcrypt.compare(pass, result[0].password, function(err, result1) {
if(result1 == true){
return true;
}
else{
return false;
}
});
}
else {
return false;
}
});
return ???;
}
I have code like this and I don't know how to make this function return the value of the compare function (true or false). Add return in child function like I did seem not to work. Can somebody help me please.

You could return a promise:
async function checkAcount(usr, pass) => {
const sql = "SELECT * FROM account WHERE userName = ?" ;
return new Promise((resolve, reject) => {
con.query(sql, [usr], (err, result) => {
if(err) {
reject(err);
throw err;
}
if(result.length > 0){
bcrypt.compare(pass, result[0].password, function(err, result1) {
if(result1 == true){
resolve(result);
return true;
} else{
reject(err);
return false;
}
});
} else {
reject(err);
return false;
}
});
});
}
Don't build your SQL query with string concatenation. That allows SQL injection.

bcrypt returns a promise
https://www.npmjs.com/package/bcrypt#with-promises
bcrypt.compare(pass, result[0].password).then((result) => {
return result;
})

How to pass value from asynchronous function (Node.js) [duplicate]

This question already has answers here:
How do I return the response from an asynchronous call?
(41 answers)
Closed 5 years ago.
From my code, I want the value in _status variable after query and write file from MongoClient.connect, but I get NULL from return _status. How can I pass the value outside the function? Thank you for your answer.
function query(domain)
{
var _status;
MongoClient.connect(url, function(err, db) {
if (err) throw err;
db.collection("zone").find({"name" : domain}).toArray(function(err, result) {
if (!err) {
fs.writeFile('/root/'+domain+'.txt', result, function (err) {
if (err) throw err;
});
_status = "success";
}
else {
_status = "fail";
}
});
db.close();
});
return _status;
}

You are calling asynchronous functions( MongoClient.connect, .find) inside your function query, and trying to get the result(_status) synchronously. This does not work. You can use a callback based approach or a promise based approach to let the value of _status known to the caller.
Please refer here for more on promises.

try something like that
function query(domain, callback)
{
var _status;
MongoClient.connect(url, function(err, db) {
if (err) throw err;
db.collection("zone").find({"name" : domain}).toArray(function(err, result) {
if (!err) {
fs.writeFile('/root/'+domain+'.txt', result, function (err) {
if (err) throw err;
});
_status = "success";
}
else {
_status = "fail";
}
callback(_status);
});
db.close();
});
}
query(domain, (status) => {
// Synchronous
// do something
console.log(status);
});

Pass object from SQL query function to a separate function [duplicate]

This question already has answers here:
How do I return the response from an asynchronous call?
(41 answers)
Closed 5 years ago.
I'm new to node and promises. I have two files - server.js and db.js
server.js imports db.js as modules.
I'm fetching some data from a SQL database in a db.js module and I'm trying to pass that data to a function in server.js.
I've successfully fetched the data from database, but when I try to pass it to the function in server.js, it only returns an undefined value.
Here's the code
server.js
const db = require('./db.js');
app.post('/api/trigger-push-msg/', function (req, res) {
return getSubscriptionsFromDatabase()
.then(function(subscriptions) {
// Do something
});
});
function getSubscriptionsFromDatabase() {
return new Promise((resolve, reject) => {
let subscriptions = db.getSubscriptions();
console.log(subscriptions); // this only prints "undefined"
if (subscriptions != undefined) {
resolve(subscriptions);
} else {
reject("No"); // this executes
}
})
}
db.js
module.exports = {
getSubscriptions: function() {
var sql = "SELECT * FROM subscriptions";
con.query(sql, function(err, result) {
if (err) throw err;
console.log(result); // this prints the same result as I want
return result;
})
}
}

getSubscriptions doesn't have a return statement
and considering that there's some async content in it you should wrap all inside a promise and trigger the subsequent logic only after it resolves.
module.exports = {
getSubscriptions: function() {
var sql = "SELECT * FROM subscriptions";
return new Promise(function(resolve, reject){
con.query(sql, function(err, result) {
if (err) return reject(err);
resolve(result);
})
})
}
}
then:
function getSubscriptionsFromDatabase() {
return db.getSubscriptions()
.then(function(subscriptions){
return subscriptions;
})
}
and in your route:
app.post('/api/trigger-push-msg/', function (req, res) {
getSubscriptionsFromDatabase()
.then(function(subscriptions) {
res.send(subscriptions);
})
.catch(function(err){
res.sendStatus(500);
})
});

JavaScript/NodeJS Callback within a callback [duplicate]

This question already has answers here:
How do I return the response from an asynchronous call?
(41 answers)
Closed 6 years ago.
I'm using the 'user-management' package in Node, and I have a callback within a callback, within a callback. But the final result doesn't return. This is my main NodeJS module:
playerManagement.login(data.username, data.pw, function (result) {
console.log(result) <-- statement never reached
if (result == "fail") {
socket.emit('client', { type: 'login', result : 'fail'});
} else {
connections[playerindex++] = {'username' : username, 'sockid' : socket.id, 'token' : result };
socket.emit('client', { type: 'login', result : 'success', username : username });
console.log(connections);
}
});
Then I have an external module with the function:
playerModule.prototype.login = function(username, password) {
var o = this;
o.user.load(function (err) {
if (!err) {
o.user.authenticateUser(username, password, function(err, result) {
if (!result.userExists) {
console.log('Invalid username');
return "fail";
} else if (!result.passwordsMatch) {
console.log('Invalid password');
return "fail";
} else {
console.log('User token is: ' + result.token); <--- this is reached.
return result.token;
}
});
} else {
console.log('error logging in');
return "fail";
}
});
So I'm guessing I need to return the value to the "load" function callback, but I'm not sure how to do that.

Change the definition of login with the following.
playerModule.prototype.login = function(username, password, callback) {
var o = this;
o.user.load(function (err) {
if (!err) {
o.user.authenticateUser(username, password, function(err, result) {
if (!result.userExists) {
console.log('Invalid username');
return callback("fail");
} else if (!result.passwordsMatch) {
console.log('Invalid password');
return callback("fail");
} else {
console.log('User token is: ' + result.token); <--- this is reached.
return callback(result.token);
}
});
} else {
console.log('error logging in');
return callback("fail");
}
});

Returning variable from callback into a defined function-NodeJS [duplicate]

This question already has answers here:
How do I return the response from an asynchronous call?
(41 answers)
Closed 6 years ago.
music.playsong = function(vars){
//vars is an array with a Key named "song"
youTube.search(vars["song"], 2, function(error, result) {
if (error) {
console.log(error)
return;
}else {
console.log("Success")
return result
}
})
}
I am currently calling this function as
music.playsong(data)
However in this function I can not access the underlying callback and get the value from that. How do I get this music.playsong() to return the result of the callback without blocking execution?

You want use a async function as sync. So it's not possible. So you need to change your method to be async like this :
music.playsong = function(vars, cb){
//vars is an array with a Key named "song"
youTube.search(vars["song"], 2, function(error, result) {
if (error) {
console.log(error)
process.nextTick(() => {
cb(error)
})
}else {
console.log("Success")
process.nextTick(() => {
cb(null, result)
})
}
})
}

music.playsong = function(vars){
youTube.search(vars["song"], 2, function(error, result) {
if (error) {
return callback("Error",{});
}else {
console.log("Success")
return callback(""success",result)
}
})
}
function callback(data){
//TODO
}

It looks like that youtube.search is an asynchronous action.
In this case, you should use Promise
e.g.
music.playsong = function(vars) {
return Promise(resolve, reject) {
//vars is an array with a Key named "song"
youTube.search(vars["song"], 2, function(error, result) {
if (error) {
return reject(err);
}
console.log("Success")
return resolve(result);
}
})
}
}
music.playsong('').then(function(result) {
// you will get result here
});
In Promise, you will have resolve and reject for handling async action.
when resolve got called, it will pass data to .then
when reject got caleed, it will pass err to .catch