问提交注册表时使用jQuery显示错误

EN

//changing the init of the $data array
$data = array();
if( isset($fn) && isset($ln) ) {
 if( $fn != "" && $ln!="" && $fn == $ln ) {
   $data["flname"] = "cntbempty";
  }
}
/* List of all your validation tests */

//Now your test if you have any errors in your $data
if(!empty($data))
{
    echo json_encode($data);
    die;
}

//And only after if the condition is not met, you can insert and redirect
/* Rest of your code here */

//example
if( data.flname && data.flname == "cntbempty" )
    $("p#name_error").slideDown();

$(document).ready(function(){
  $("form.register").submit(function(e) {
    e.preventDefault();
    $.post("register.php", $("form.register").serialize(), function( data ) {
      if(data.length == 0){
        window.location.href= "login.php";
      }

      if( data.flname == "cntbempty" )
        $("p#name_error").slideDown();
      else
        $("p#name_error").hide();
      if( data.username == "inuse" )
        $("p#username_error").slideDown();
      else
        $("p#username_error").hide();
      if( data.password == "missmatch" )
        $("p#password_error").slideDown();
      else
        $("p#password_error").hide();
      if( data.email == "notvalid" )
        $("p#email_error").slideDown();
      else
        $("p#email_error").hide();
    }, "json");
  });
});

<?php
 if(isset($_POST['reg'])){
   $fn = ucfirst($_POST['fname']);
   $ln = ucfirst($_POST['lname']);
   $un = $_POST['username'];
   $em = $_POST['email'];
   $pswd = $_POST['password'];
   $pswd2 = $_POST['password2'];

   $sql=$db->prepare("SELECT username FROM users WHERE username=:username");
   $sql->execute(array(':username'=>$un));
   $row = $sql->fetch(PDO::FETCH_ASSOC);
   $db_username = $row['username'];
   $usernames = $db_username;

   //$data = array();
     $data = 0;
   if( isset($fn) && isset($ln) ) {
    if( $fn != "" && $ln!="" && $fn == $ln ) {
      // $data["flname"] = "cntbempty";
         $data = 2;
    }
  }
  if( isset($un) ) {
    if $un == $usernames )  {
     // $data["username"] = "inuse";
        $data = 3;
}
}
if( isset($pswd) && isset($pswd2) ) {
  if( $pswd2 != "" && $pswd != $pswd2 ) {
    // $data["password"] = "missmatch";
       $data = 4;
  }
}
if( isset( $em ) ) {
 if( $em != "" && !preg_match( "/^([a-zA-Z0-9])+([a-zA-Z0-9\._-])*@([a-zA-Z0-9_-])+([a-zA-Z0-9\._-]+)+$/", $_POST["email"] ) ) {
   // $data["email"] = "notvalid";
      $data = 5;
 }
}
/* if(!empty($data))
{
  header('Content-Type: application/json');
  echo json_encode($data);
  die;
}
else{ */ 

  $pswd = password_hash($pswd, PASSWORD_DEFAULT);
  $pswd2 = password_hash($pswd2, PASSWORD_DEFAULT);
  $stmt = $db->prepare("INSERT INTO users (username,first_name,last_name,email,password,password2,) VALUES (:username,:first_name,:last_name,:email,:password,:password2,)");  
  $stmt->execute( array(':username'=>$un,':first_name'=>$fn,':last_name'=>$ln,':email'=>$em,':password'=>$pswd,':password2'=>$pswd2));
// }
//! Send Success Status to browser for it to understand
if ($stmt->rowCount() == 1) {
  // $data['success'] = true;
     $data = 1;
} 
else {
  // $data['success'] = false;
  $data = -1;
}
// header('Content-Type: application/json');
// echo json_encode($data);

echo $data;

}
?>

$(document).ready(function(){
  $("form.register").change(function() {

   var data = new FormData(this);

    $.ajax({
        type:"post",
        url: register.php,
        data:data,
        mimeType:"multipart/form-data",
        contentType: false,
        cashe: false,
        processData: false,
        error:function(data){
            alert ("An Error has Occured...");
            return false;
        },
        beforeSend: function() {
            $('#Loading').html('<img src="images/page-loader.gif" />&nbsp;&nbsp;Processing</div>');

        },
        success: function(html){
            switch($html){
                case 1:
                      alert("success");
                       window.location.href="" /* your redirect page*/;
                      break;
                      case 2:
                        $("#error").html('Field cannot be Empty !!!');
                      break;
                      case 3:
                        /* so on...*/
                      break;
                      case 4:
                      break;
                      case 5:
                      break;

            }
        }
    });
  });
});