How can I work on the output of jsonp in phonegap?

I am working on a PhoneGap with Android project. I have designed a login page in which I want to show an alert box for a valid and in开发者_如何学运维valid user. I am using PHP for database validation.

This is my php page:

<?php
    header('Content-type: application/json');

    $server = "localhost";
    $username = "root";
    $password = "";
    $database = "mymusic";

    $con = mysql_connect($server, $username, $password) or die ("Could not connect: " . mysql_error());
    mysql_select_db($database, $con);
     $id=$_GET["id"];
     $pass=$_GET["password"];
    //$id='ram';
    //$pass='ram';
    $sql = "SELECT id, name,password FROM login where userid='$id' and password='$pass'";
    $result = mysql_query($sql) or die ("Query error: " . mysql_error());

    $records = array();

    while($row = mysql_fetch_assoc($result)) {
        $records[] = $row;
    }

    mysql_close($con);

    echo $_GET['jsoncallback'] . '(' . json_encode($records) . ');';
    ?>

This is my java script function:

 function onDeviceReady(){
        var output = $('#output');
        var id = document.getElementById('userid').value;
        var pass = document.getElementById('password').value;
       // webcam.set_api_url( 'test.php?filename=' + escape(filename));

        $.ajax({
            url: 'http://192.168.1.214/sample/dologin.php?id='+id+'&password='+pass,
            dataType: 'jsonp',
            jsonp: 'jsoncallback',
            timeout: 5000,
            success: function(data, status){
                console.log('entered success============');
                $.each(data, function(i,item){ 

                var logi=item.id;
                if(logi!=null)
                    alert("valid user");
                else
                    alert("invalid user");

                });

            },
            error: function(){
                console.log('entered success====================');
               output.text('There was an error loading the data.');
            }
        });
 }

This is not working properly for an invalid user. Whenever I enter a valid user name and password then it displays the valid user message box. When I enter an invalid user name and password then it doesn't display anything.

Thank you in advance...

Try debugging this in a browser and perhaps send the returned jsonp data to the console from within your ajax's success call console.log(data).

It's quite possible that your jsonp is returning some data as opposed to null... even if it is simply undefined or an empty string. Your conditional is most likely the culprit.