表单POST之后的PHP重定向

Question

i'm making a download button on my website that opens a modal with a request for password and then if the password is right should take the user to the real download. This is my javascript:

function submit() {

    var postData = $("#passwd").serialize();
    //alert(postData);
    $.ajax({
        type: "POST",
        url: "http://www.redcraft.it/submit.php",
        data: postData,
        success: function(redirect) {
            alert('Submitted')
        }/*,
        error: function() {
            alert('Failure');
        }*/
    });
}

and this is my php:

<?php
function redirect() {
    $data = $_POST["postData"];
    if($data == is_null()) {
        echo "Error";
    } else {
        echo "<script>window.open('http://www.google.com/" + $data + "', '_self')</script>";
    }
}
?>

I'm using echo with a js script in php to try different methods to redirect since header() doesn't work. I'm sure the php is correctly called because i've added a row to create a file when the function is called, and the file is correctly generated.

Please, i need your help and don't kill me if i've made some "noobie" errors.

Edit:

This is the html of the modal:

<div class="modal fade bs-modal-sm" tabindex="-1" role="dialog" aria-labelledby="loginModalLabel" aria-hidden="true">
            <div class="modal-dialog modal-mediom">
                <div class="modal-content">
                    <div class="modal-header">
                        <button type="button" class="close" data-dismiss="modal">&times;</button>
                        <h4 class="modal-title">Download mondo RedCraft</h4>
                    </div>
                    <div class="modal-body">
                        <p>Per scaricare il mondo della redcraft inserisci la password che trovi nel video di presentazione del download!</p>
                        <div class="control-group">
                            <label class="control-label" for="userid">Password:</label>
                            <div class="controls">
                                <input id="passwd" required="" name="passwordinput" type="input" class="form-control input-medium">
                            </div>
                        </div>
                        <div class="control-group">
                            <label class="control-label" for="confirmsignup"></label>
                            <div class="controls">
                                <button id="confirm" onClick="submit()" name="confirmsignup" class="btn btn-primary" data-dismiss="modal">Conferma</button>
                            </div>
                        </div>
                    </div>
                </div>
            </div>
        </div>

Answer 1

just add one div in your html

<div id="outputredirect"></div>

and add below line in your ajax success or replace with your alert

if(redirect == "Error"){
   alert(redirect);
} else {
   jQuery('#outputredirect').html(redirect);
}

Answer 2

Your javascript code should redirect to the url returned by the php script :

function submit() {
    var postData = $("#passwd").serialize();
    //alert(postData);
    $.ajax({
        type: "POST",
        url: "http://www.redcraft.it/submit.php",
        data: postData,
        success: function(redirect) {
            location.href(redirect);
        }/*,
        error: function() {
            alert('Failure');
        }*/
    });
}