jquery mobile function not returning value

I'm trying to run a check on a webdb running on a cordova/jQuery-mobile application:

This function will check whether the table exists in the DB and subsequently return a true or false. I have tried to change the return type from boolean to integer (0 and 1) but with no success.

function checkConfigTable(tablename) {
  db.transaction
  (
       function (tx)
       {
            tx.executeSql
            (
                'SELECT name FROM sqlite_master WHERE type="table" AND name=?',
                [tablename],
                function(tx,results)
                {
                    var len = results.rows.length;
                    if(len>0)
                    {
                            return true;
                    }
                    else {
                            return false;
                    }
                }, errorCB
            );
       },errorCB,successCB
   );   
}

I want to then call checkConfigTable from this other one just to alert the return value (only for test purposes at the moment) but I am always getting "undefined" as return value.

// Function to retrieve current login config
function getSavedLogin(configid) {
    var x = checkConfigTable("config");
    alert('table: ' + x);
}

If I substitute the return with an alert directly in checkConfigTable() the correct values are shown in the alert box.