Coffeescript snippet for use with jQuery-File-Upload that works with the iframe transport plugin as well as ajax which means it works in IE9 as well as Chrome etc.

file_upload.js.coffee

$form.fileupload
  dataType: "json"
  done: (e, data, extra) ->
    result = if data.result?
      data.result
    else
      data = JSON.stringify(data).replace(/"name":"utf8","value":"[^"]*"/, '"name":"utf8","value":"REMOVED"')
      JSON.parse(data).result
    console.log result

my_controller.rb

class MyController < ApplicationController

  def my_action
    # Do whatever you need to do
    respond_to do |format|
      format.js { render json: to_json(@agent) }
      format.html { render text: "<textarea data-type=\"application/json\">#{to_json(@agent)}</textarea>" }
    end
  end
  
end