$.ajax returns 0 as HTTP error code instead of 404

$.ajax returns 0 as HTTP error code instead of 404

Below is my ajax call from the HTML page.  Its actually a ajax call from an interation block.

In this I am expecting that a couple URLs will fail with HTTP code as 404.

From FireFox Net console i could see that the HTTP status as 404.  But the jqXHR.status is 0 (zero).

Could somebody please explain why its return 0 when the actual HTTP response is 404?
  2. $.ajax({
  3.         url: serviceURL,
  4.         type: "POST",
  5.         async: true,
  6.         crossDomain: true,
  7.         contentType: "text/xml",
  8.         context: tdObject,
  9.         dataType: "jsonp",
  10.         origin:window.location.protocol + "//" + window.location.host,
  11.         timeout:5000,
  12.         success: function(data){
  13.         //console.log("SUCCESS for ajax call ");
  14.         httpStatusCode=data.responseCode;
  15.   //return data.responseCode;
  16.         },
  17.         error:function(jqXHR, textStatus, errorThrown){
  18.         //console.log("Error for ajax call "+jqXHR.status+"-- "+textStatus+"--"+errorThrown);
  19.         httpStatusCode=jqXHR.status;
  20.         //return jqXHR.status;
  21.         }
  22.     });