JavaScript - passing variable from one function to another is undefined - sqlite

Question

in my example I'm trying to pass a variable (var ttoken) from one function to another and save it to the SQLite. The coding environment is Phonegap (for android). Here is the procedure:
var ttoken; // global var declaration
function handleLogin() {
var form = $("#loginForm");
var u = $("#username", form).val();
var p = $("#password", form).val();
if(u!= '' && p!= '') {
$.post("http://localhost/login.php", {username:u, password:p}, function(data){
if(data!='') {
$.mobile.changePage("change_page.html");
ttoken = data.token;
} else {
navigator.notification.alert("Error try again", function() {});
}
}, "json");
} else {
navigator.notification.alert("Error, fields are emty", function() {});
}
return {tkn:ttoken}; // putting into array
openDB();
populateDB();
}
var db;
function openDB(){ // create database
// 'Kurskoffer_DB' vol. 300 Kb
db = window.openDatabase("Sample_DB", "1.0", "Samole DB", 300000);
db.transaction(populateDB, errorCB, successCB);
}
function populateDB(tx){ // create 'settings' table
var tooken = handleLogin(); // accessing the variable ttoken
tx.executeSql('CREATE TABLE IF NOT EXISTS settings (id INTEGER PRIMARY KEY, token TEXT NOT NULL, sound TEXT NOT NULL, vibra TEXT NOT NULL)');
tx.executeSql('INSERT INTO settings(id, token, sound, vibra) VALUES (1, "'+tooken.tkn+'", "on", "on")');
}
Seems everything according variable passing rule is ok, but the insert result in the table for field token is undefined. Have anyone idea why this is happening? Thanks.

Answer 1

The $.post function is asynchronous, which means handleLogin will return before the post callback has fired, and ttoken remains undefined in the returned object.
Set up handleLogin to accept a callback, which will fire when the post has returned and ttoken has been populated.
Something like:
function handleLogin(callback) {
var form = $("#loginForm");
var u = $("#username", form).val();
var p = $("#password", form).val();
if(u!= '' && p!= '') {
$.post("http://localhost/login.php", {username:u, password:p}, function(data){
if(data!='') {
$.mobile.changePage("change_page.html");
ttoken = data.token;
if (callback) callback();
} else {
navigator.notification.alert("Error try again", function() {});
}
}, "json");
} else {
navigator.notification.alert("Error, fields are emty", function() {});
}
}
function populateDB(tx){ // create 'settings' table
handleLogin(function() {
tx.executeSql('CREATE TABLE IF NOT EXISTS settings (id INTEGER PRIMARY KEY, token TEXT NOT NULL, sound TEXT NOT NULL, vibra TEXT NOT NULL)');
tx.executeSql('INSERT INTO settings(id, token, sound, vibra) VALUES (1, "'+ttoken+'", "on", "on")');
});
}
Since ttoken is defined globally you don't have to worry about passing it around as an argument.