a selenium helper.rb

module SeleniumHelpers
  # Execute JavaScript in the context of your Selenium window
  def run_javascript(javascript)
    driver.get_eval <<-JS
      (function() {
        with(this) {
          #{javascript}
        }
      }).call(selenium.browserbot.getCurrentWindow());
    JS
  end
  
  private
  
  # If running in regular Selenium context, get_eval is defined on self.
  def driver
    respond_to?(:selenium) ? send(:selenium) : self
  end
end

regular selenium usage.rb

class JavaScriptHelperTest < ActiveSupport::TestCase
  include SeleniumHelpers
  include ElementHelpers
  
  def setup
    @element = locate('#all')
  end
  
  def test_visible_by_default
    assert @element.visible?
  end
  
  def test_hide_element
    @element.hide!
    assert ! @element.visible?
  end
  
  def test_show_element
    @element.hide! # setup
    @element.show!
    assert @element.visible?
  end
end

selenium element helper.rb

module ElementHelpers
  class Element
    def initialize(context, selector)
      @context, @selector = context, selector
    end
    
    def hide!
      call(:hide)
    end
    
    def show!
      call(:show)
    end
    
    def visible?
      call(:is, ':visible') == 'true'
    end
    
    private
    
    def call(fn, *args)
      @context.run_javascript <<-JS
        return jQuery(#{@selector.inspect})[#{fn.to_s.inspect}](#{args.map(&:inspect).join(', ')});
      JS
    end
  end
  
  def locate(selector)
    Element.new(self, selector)
  end
end

webrat usage.rb

When /^I click "(.*)"$/ do |text|
  run_javascript <<-JS
    jQuery('*:contains("#{text}")').click();
  JS
end