Jquery/AJAX response - Works in FF/Safari but not IE parseFloat(html) problem?

Question

I have a JQuery/Ajax update. It correctly updates in all major browsers, however, dealing with error responses does not work in any version of IE.

Heres the ajax submit code:

    $('.ajax_multi_submit').click(function(event){
 // if javascript is enabled, stop default post
 event.preventDefault();

 // get the id assigned to this form. This id will
 // be added to every id to used in processing
 var element = $(this);
 var Id = element.attr("id");  
 var formUrl = $('#ajax_multi_form'+Id).attr('action'); 

 $.ajax({
   url: formUrl,
   type: "POST",
   dataType: "html",
   data: $('#ajax_multi_form'+Id).serialize(),
   beforeSend: function(){
    showAjaxMultiBusy(Id);
   },
   complete: function(){
   },
   success: function(html){
    processAjaxMultiForm(html, Id);
   }
  }); 
});

Again, I don't think the problem is here, as all browsers post updates correctly. However, when processing the result with this code:

    function processAjaxMultiForm(html, Id){

 $('#ajax_errors'+Id).hide('slow');

 window.setTimeout( function(){

   $('#ajax_busy'+Id).hide('slow');

   if (parseFloat(html)){
    $('#ajax_message'+Id).html('Record Saved.').show('normal');
    $('#ajax_message'+Id).hide('slow');
   }else{

    $('#ajax_errors'+Id).html(html).show('slow');
   }
 }, 1500);
}

When an error string is returned instead of an integer ( parseFloat(html) = "some string..." ), FF and Safari correctly display the error in the "else" condition.

IE will always display the "if" condition, regardless of return value (1=success, string=error).

I assume some genius out there will see the problem immediately?

EDIT ------- Here's a bit more info. I added a console log to the script to output the html variable. I am getting a proper string on errors, and a "1" on success. I've updated the code per a suggestion below to:

function processAjaxMultiForm(html, Id){

$('#ajax_errors'+Id).hide('slow');

window.setTimeout( function(){

$('#ajax_busy'+Id).hide('slow');

console.log("html is: " +html);

if (isNaN(html)){
 $('#ajax_errors'+Id).html(html).show('slow');

}else{
 $('#ajax_message'+Id).html('Record Saved.').show('normal');
 $('#ajax_message'+Id).hide('slow');
}

}, 1500); }

As before, works as expected in FF Safari, but IE evaluates both string (error) and integer (success) as a "success"

Answer 1

isNan should work.

Answer 2

How about trying (isNan(parseFloat(html)).

EDIT:

Alternatively why don't you return "Success" to aid in clarity.