Formtastic Datepicker field.

application.js

$(function() {
    $("INPUT.datepicker").datepicker();
}

input_datepicker.rb

class DatepickerInput < Formtastic::Inputs::StringInput
  def input_html_options
    unless object.nil?
      value = I18n.l(object.send(method))
    else
      value =""
    end
    super.merge(:class => "#{super[:class]} datepicker", :value => value)
  end
end

how do I use this in a rails application?