Hello I have a form that submits remotely with the jQuery UJS for rails. I binded to the beforeSend event to allow me to modify the data submitting to the serve. It's not working. Here is what I have in the beforeSend:

 settings.data = JSON.stringify({
      'list_item[title]' : 'hi?? there'
 })

This doesn't work. In the server logs I see this:

Started POST "/lists/9/list_items" for 127.0.0.1 at 2011-10-24 14:04:36 -0700
  Processing by ListItemsController#create as JSON
  Parameters: {"{\"list_item"=>{"title"=>{"\":\"hi?? there\"}"=>nil}}, "list_id"=>"9"}

Any idea what I'm doing wrong? I want to customize the settings.data with added fields that aren't in the form. Thanks

You don't need to stringify anything to put it in settings.data. The data is:

Data to be sent to the server. It is converted to a query string, if not already a string. It's appended to the url for GET-requests. [...] Object must be Key/Value pairs.

What you're doing is putting this string:

"{"list_item[title]":"hi?? there"}"

into data but that string is not a query string so things are going to get confused. You should be able to simply assign your JavaScript object to settings.data:

settings.data = { 'list_item[title]' : 'hi?? there' };

and let jQuery sort it out from there.

Update based on evidence rather than documentation:

However, further investigation reveals that this doesn't work. If I send a GET request, any changes I make to settings.data are ignored but if I send a POST request, then changes to settings.data stick but you have to use the query string format to get anything sensible through:

settings.data = encodeURIComponent('list_item[title]')
              + '='
              + encodeURIComponent('hi?? there');

The version of settings.data combined with a POST request gets me this:

Parameters: {"list_item"=>{"title"=>"hi?? there"}}

on the server and that looks like what you're after. If you want to preserve some of the original parameters then you'll have to unpack and repack the query string by hand.