    # File lib/action_view/helpers/prototype_helper.rb, line 1091
          def build_callbacks(options)
            callbacks = {}
            options.each do |callback, code|
              if CALLBACKS.include?(callback)
                name = 'on' + callback.to_s.capitalize
                callbacks[name] = "function(request){#{code}}"
              end
            end
            callbacks
          end