working - submit form using jquery ajax serialize

How to add data via $.ajax(serialize()+extra data)like this (2)

Personally, I'd append the element to the form instead of hacking the serialized data, e.g.

moredata = 'your custom data here';

// do what you like with the input
$input = $('<input type="text" name="moredata"/>').val(morevalue);

// append to the form

// then..
data: $('#myForm').serialize()

That way, you don't have to worry about ? or &

I want to add extra data after i use $('#myForm').serialize() + extra data

   type: 'POST',
   url: $('#myForm').attr('action'),
   data: $('#myForm').serialize(),   // I WANT TO ADD EXTRA DATA + SERIALIZE DATA
   success: function(data){

What kind of data?

data: $('#myForm').serialize() + "&moredata=" + morevalue

The "data" parameter is just a URL encoded string. You can append to it however you like. See the API here.