ajax提交错误捕获

I'm having trouble getting ajaxSubmit to catch an error:

$(document).ready(function(){

        $("#supportForm").validate({
              rules: {
                 //validation
              },

              messages: {              
                 //messages
              },

              submitHandler: function(form) {
                    $(form).ajaxSubmit({
                        url:"ajax/supportform",
                        type:"GET",
                        dataType: 'json',
                        error: function() { alert('error'); },
                        success: function() {alert('success'); },


                    });
              }

        });  
    })

what do I have to return in my php script to get it to fire the error event?

I've tried returning an array with error=>0 , exit(json_encode('error'=>'0'); etc.

Edit: to show some specific error description coming from PHP you should read this question: jQuery Ajax error handling, show custom exception messages

Let your server generate some error, with PHP you can do that like this

<?php
header("HTTP/1.0 404 Not Found");
?>

Check out the documentation of the header function: http://nl.php.net/manual/en/function.header.php

What you are doing here is providing your webbrowser with data that does not belong in the typical HTML source, by which the webbrowser knows something went wrong.

You could actually add all meta data you want to the header of the webpage request, but when the webbrowser does not know what it means it is simply ignored. See the definition or status codes here: http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html

change url to something that doesn't exist to force an error

          function(form) {
                $(form).ajaxSubmit({
                    url:"ajax/supportform001",
                    type:"GET",
                    dataType: 'json',
                    error: function() { alert('error'); },
                    success: function() {alert('success');} // <-was an extra comma
                });
          }

See Mike de Klerk's link, it provided the clues as to what had to be done to trap an error:

It seems the success & error callbacks have nothing to do with passing a boolean error/success message, but only if the url was successfully called. I expect I am not getting error results as I am using a CMS that is always returning some kind of content - even if it's a 404 or 403 page.

Anyway, I had to return a json string from my php script:

<?php


$response = json_encode(array("error" => "false","message" => "this is the error message"));

return $response;

then parse it in my success callback:

submitHandler: function(form) {
        $(form).ajaxSubmit({
            url:"ajax/supportform",
            type:"POST",
            dataType: 'json',

            error: function(data ) { alert(data); },

            success: function(response) {

            var obj = jQuery.parseJSON(response);

            if(obj.error == "true"){
                alert('error is true');
            }else{
                alert('error is false')
            }

            },


        });
  }