Custom error handling with jQuery.ajax()

ajaxOverride.js

// CUSTOM AJAX FUNCTION FOR STRUCTURED ERROR HANDLING
(function(){
  // Store a reference to the original ajax method.
  var originalAjaxMethod = jQuery.ajax;
  var EF = function(){};
  // override the default $.ajax to include special handlers for error and success
  // to utilize new custom error box. existing success and error callbacks are
  // left intact and given the expected params.
  jQuery.ajax = function(options) {
    var thisSuccess = (typeof options.success == 'function') ? options.success : EF;
    var thisError = (typeof options.error == 'function') ? options.error : EF;
    options.success = function(data,status,xhr) {
      // do check here to see if there are errors
      var theError = "";
      var theMessage = "";
      if (options.dataType == 'json') {
        if (data.ERROR) {
          theError = data.ERROR;
        } else if (data.REDIRECT) {
          window.location = data.REDIRECT;
          return true;
        } else if (data.MESSAGE) {
          theMessage = data.MESSAGE;
        }
      // if the response is html, look for $('.display-error') and $('.display-message')
      } else if (options.dataType == 'html') {
        var thisResponse = $('<div>'+data+'</div>');
        if (thisResponse.find('.display-error').length > 0) {
          theError = thisResponse.find('.display-error').text();
        } else if (thisResponse.find('.display-message').length > 0) {
          theMessage = thisResponse.find('.display-message').text();
        }
      }
      if (theError == "") {
        // if not, run passed in success callback:
        thisSuccess(data,status,xhr);
        // if there is a message, display it now
        if (theMessage != "") {
          SpecifyHandleMessage(theMessage);
        }
      } else {
        // there is an error, display it up top, don't execute the callback.
        SpecifyHandleError(theError);
        thisError(xhr,status,data);
      }
    };
    options.error = function(xhr,status,error) {
      SpecifyHandleError("There was an error with the request. Our team has been notified - you can rest assured that we are already looking into it!");
      // also execute error callback, if one has been passed in:
      thisError(xhr,status,error);
    };

    // Execute the original ajax.
    return originalAjaxMethod(options);
  }
})();