使用web数据库的Phonegap错误:"表达式mydb的结果.事务不是一个函数

我第一次尝试在iOS应用中使用phonegap使用html5的web数据库。但是我被这个错误卡住了，它说"表达式mybd的结果"。事务不是函数"

如果我使用警报检查，initDB正在执行，但当涉及到createTables函数时，上述错误上升，我对此无能为力。

我已经使用了这个实现-> http://wiki.phonegap.com/w/page/16494756/Adding%20SQL%20Database%20support%20to%20your%20iPhone%20App

<script type="text/javascript">
    function validateFloat()
    {
        var mydb=false;
        var fuelUnits = document.myForm.UnitsOfFuel;
        var bFuelUnits = false;
        var bUnitPrice = false;
        switch (isNumeric(fuelUnits.value))
        {
            case true:
            bFuelUnits = true;
            fuelUnits.style.background="white";
            break;
            case false:
            fuelUnits.focus();
            fuelUnits.style.background="yellow";
            break;
        }
        var unitPrice = document.myForm.PricePerUnit;
        switch (isNumeric(unitPrice.value))
        {
            case true:
            bUnitPrice = true;
            unitPrice.style.background="white";
            break;
            case false:
            unitPrice.focus();
            unitPrice.style.background="yellow";
            break;
        }
        if(bFuelUnits && bUnitPrice)
        {
            if(initDB(mydb))
            {
                if(createTables(mydb))
                {   
                    loadCelebs();
                    return true;
                }
                else
                    return false;
            }
            else
                return false;
        }
        else
        {
            return false;
        }
    }
    function isNumeric(n)
    {
        var n2 = n;
        n = parseFloat(n);
        return (n!='NaN' && n2==n);
    }
    // initialise the database
    function initDB(mydb) 
    {
        try 
        { 
            if (!window.openDatabase) 
            { 
                alert('not supported'); 
                return false;
            } 
            else 
            { 
                var shortName = 'phonegap'; 
                var version = '1.0'; 
                var displayName = 'PhoneGap Test Database'; 
                var maxSize = 65536; // in bytes 
                mydb = openDatabase(shortName, version, displayName, maxSize);
                alert("initDB");
                return true;
            }
        } 
        catch(e) 
        { 
            // Error handling code goes here. 
            if (e == INVALID_STATE_ERR) 
            { 
                // Version number mismatch. 
                alert("Invalid database version."); 
                return false;
            } 
            else 
            { 
                alert("Unknown error "+e+"."); 
                return false;
            } 
            return true; 
        } 
    }
    // db error handler - prevents the rest of the transaction going ahead on failure
    function errorHandler(transaction, error) 
    { 
        alert("errorHandler");
        // returns true to rollback the transaction
        return true;  
    }
    // null db data handler
    function nullDataHandler(transaction, results) 
    { 
    } 
    // create tables for the database
    function createTables(mydb) 
    {
        try 
        {
            mydb.transaction(
                             function(tx) {
                             tx.executeSql('CREATE TABLE celebs(id INTEGER NOT NULL PRIMARY KEY, name TEXT NOT NULL DEFAULT "");', [], nullDataHandler(tx,results), errorHandler(tx,error)); 
                             tx.executeSql('insert into celebs (id,name) VALUES (1,"Kylie Minogue");', [], nullDataHandler(tx,results), errorHandler(tx,error)); 
                             tx.executeSql('insert into celebs (id,name) VALUES (2,"Keira Knightley");', [], nullDataHandler(tx,results), errorHandler(tx,error)); 
                             });
            alert("createTables");
            return true;
        } 
        catch(e) 
        {
            alert(e.message);
            return false;
        }
    }
    // load the currently selected icons
    function loadCelebs()
    {
        try 
        {
            mydb.transaction(
                function(tx) {
                tx.executeSql('SELECT * FROM celebs ORDER BY name',[], celebsDataHandler(tx,results), errorHandler(tx,error));
                });
        } 
        catch(e) 
        {
            alert(e.message);
        }
    } 

    // callback function to retrieve the data from the prefs table
    function celebsDataHandler(transaction, results) 
    {
        alert("here also?");
        // Handle the results 
        var html = "<ul>"; 
        for (var i=0; i<results.rows.length; i++) 
        { 
            var row = results.rows.item(i); 
            html += "<li>"+row['name']+"</li>'n";
        } 
        html +="</ul>";
        alert(html);
    }
</script>