Adds flash messages to the response header so they can be picked up via js.

flash_header.rb

after_filter :add_flash_messages
  
# Adds flash messages to the HTTP headers so they can be used on the current request with AJAX
def add_flash_messages
  return true unless response.content_type.to_s.match(/javascript/i)
  return true if flash.keys.empty?
  response.headers['X-Flash-Messages'] = flash.to_json
  flash.discard
end

flash_messages.js

// Event trigger for jquery that collects the flash messages from the header. Simply bind something to the "flash:add" event.

$(document).ajaxSuccess(add_flash_messages);

function add_flash_messages(event, xhr, settings){
	var messages = xhr.getResponseHeader('X-Flash-Messages'), divs = [];
	if(!messages) return true;
	messages = $.parseJSON(messages);
	$.each(messages, function(key, value){
		var div = $("<div></div>").addClass('flash_message')
					.addClass('flash_'+key)
					.addClass(key)
					.hide()
					.html(value+"<span>X</span>");						
		$.event.trigger('flash:add', [div]);
	});
	return true;
}