Nodejs, return condition not working [duplicate] - node.js

Question

This question already has answers here:
How do I return the response from an asynchronous call?
(41 answers)
Closed 6 years ago.
I am new to Nodejs. I am trying to return data. after select query. Here i am writing two condition's. first is very simple in logic and it is working but let me know why second condition is not working.
First Condition:
var arr = {email:"john#gmail.com", password:"};
return arr;
databaseConnection.query("SELECT * FROM users where email = '"+email+"' and password = '"+password +"'", function (err, result) {
});
Second Condition
databaseConnection.query("SELECT * FROM users where email = '"+email+"' and password = '"+password +"'", function (err, result) {
var arr = {email:"john#gmail.com", password:"};
return arr;
});
from passport.js
var LocalStrategy = require('passport-local').Strategy;
var FacebookStrategy = require('passport-facebook').Strategy;
var TwitterStrategy = require('passport-twitter').Strategy;
var configAuth = require('./auth');
module.exports = function(passport,databaseConnection) {
var usermodule = require('../models/user')(databaseConnection);
passport.serializeUser(function(user, done) {
done(null, user);
});
passport.deserializeUser(function(user, done) {
done(null, user);
});
passport.use('local-login', new LocalStrategy({
usernameField : 'username',
passwordField : 'password',
passReqToCallback : true // allows us to pass back the entire request to the callback
},
function(req, email, password, done) { // callback with email and password from our form
var user={};
var result = usermodule.login(email,password);
console.log('usercraeted');
user["email"]=email;
user["status"]=true;
user["name"]="John Snow";
user["avatar"]="";
user["loginStatus"]=true;
return done(null, user);
user["msg"]="invalide email";
console.log("out");
return done(null, false,user["msg"]);
};
);
};

Answer 1

In your first example, the code is executed up to this point:
var arr = {email:"john#gmail.com", password:"};
return arr;
// interpreter exits and `{email:"john#gmail.com", password:"}` is returned,
// `databaseConnection.query("` is never executed
In your second example, the code is executed up to this point:
databaseConnection.query("SELECT * FROM users where email = '"+email+"' and password = '"+password +"'", function (err, result) {
var arr = {email:"john#gmail.com", password:"};
return arr;
});
// interpreter exits, undefined is returned

Answer 2

The second condition doesn't work because node.js is asynchronous. And your return is on a callback that take some times to be executed.

Answer 3

You have to use callbacks.
function getUser() {
var email = "test#test.com";
var password = "test";
getDatas(email, password, function(err, result) {
// the result is good and not undefined if no errors :)
});
}
function getDatas(email, password, callback) {
databaseConnection.query("SELECT * FROM users where email = '"+email+"' and password = '"+password +"'", function (err, result) {
callback(err, result); // callback is executed with the result you
});
}
Hope I helped you