    # File lib/action_view/helpers/prototype_helper.rb, line 1069
          def build_observer(klass, name, options = {})
            if options[:with] && (options[:with] !~ /[\{=(.]/)
              options[:with] = "'#{options[:with]}=' + encodeURIComponent(value)"
            else
              options[:with] ||= 'value' unless options[:function]
            end

            callback = options[:function] || remote_function(options)
            javascript  = "new #{klass}('#{name}', "
            javascript << "#{options[:frequency]}, " if options[:frequency]
            javascript << "function(element, value) {"
            javascript << "#{callback}}"
            javascript << ", '#{options[:on]}'" if options[:on]
            javascript << ")"
            javascript_tag(javascript)
          end