Rails, javascript and updating forms

I have a form that allows the user to choose a country. Depending on which country is selected, I need to change the State/Province drop-down to include either a list of states or a list of provinces. I was going about this using the observe_fie开发者_运维知识库ld tag, but that was depreciated in rails 3...

So.., how should one go about this now? I am using select_tag to populate the drop-downs, and the arrays used in the options_for_select are all stored server-side and made accessible in the controller action, so I can't access them from javascript..

Using the Carmen gem: https://github.com/jim/carmen.

I did the following some times ago (AJAX).

HTML:

    <p>
        <label>Country <span>*</span></label>
        <%= profile_form.select(:country,Carmen.countries, {:include_blank => 'Select a Country'}, :id => "profile_country") %>
    </p>
    <p>
        <label>State <span>*</span></label>
        <%= profile_form.select(:state,  "" , {:include_blank => 'Select a Country first'}, :id => "profile_state") %>
    </p>

Controller:

def states
  begin
    render :json => Carmen::states(CGI::unescape(params[:country]))
  rescue 
    render :json => {"content" => "None"}.to_json
  end
end 

Javascript with jQuery:

$('#profile_country').change(function() {
    if ($(this).val() == '')
    {
      $('#profile_state').empty();
      $('#profile_state').append( $('<option>No state provided for your country</option>'));
    }
    else {
        $.ajax({
            type: "GET",
            url: "/remote/get_states/" + encodeURIComponent($(this).attr('value')),
            success: function(data){
                if (data.content == 'None')
                {
                    $('#profile_state').empty();
                  $('#profile_state').append( $('<option>No state provided for your country</option>'));
                }
                //handle the case where no state related to country selected
              else
             {
                $('#profile_state').empty();
                $('#profile_state').append( $('<option>Select your State</option>'));
                jQuery.each(data,function(i, v) {
                 $('#profile_state').append( $('<option value="'+ data[i][1] +'">'+data[i][0] +'</option>'));
            });
        }
        }
      });
    }
 });