以Github为例，代码如下：
require 'rubygems'
require 'watir'
require 'watir-webdriver'
b = Watir::Browser.new :firefox
b.goto "https://github.com/about"
puts b.div(:class => "column one-half").present?
puts b.div(:class => "column one-half").parent.text
得到这些输出：
[remote server] https://github.com/about line 68 > Function:17:in `H': a is undefined (Selenium::WebDriver::Error::JavascriptError)
from [remote server] https://github.com/about line 68 > Function:17:in `anonymous/</<'
from [remote server] https://github.com/about line 68 > Function:14:in `anonymous/<'
from [remote server] https://github.com/about line 68 > Function:14:in `anonymous'
from [remote server] https://github.com/about:68:in `handleEvaluateEvent'
from my_path/gems/ruby-2.1.5/gems/selenium-webdriver-2.44.0/lib/selenium/webdriver/remote/response.rb:52:in `assert_ok'
from my_path/gems/ruby-2.1.5/gems/selenium-webdriver-2.44.0/lib/selenium/webdriver/remote/response.rb:15:in `initialize'
from my_path/gems/ruby-2.1.5/gems/selenium-webdriver-2.44.0/lib/selenium/webdriver/remote/http/common.rb:59:in `new'
from my_path/gems/ruby-2.1.5/gems/selenium-webdriver-2.44.0/lib/selenium/webdriver/remote/http/common.rb:59:in `create_response'
from my_path/gems/ruby-2.1.5/gems/selenium-webdriver-2.44.0/lib/selenium/webdriver/remote/http/default.rb:66:in `request'
from my_path/gems/ruby-2.1.5/gems/selenium-webdriver-2.44.0/lib/selenium/webdriver/remote/http/common.rb:40:in `call'
from my_path/gems/ruby-2.1.5/gems/selenium-webdriver-2.44.0/lib/selenium/webdriver/remote/bridge.rb:640:in `raw_execute'
from my_path/gems/ruby-2.1.5/gems/selenium-webdriver-2.44.0/lib/selenium/webdriver/remote/bridge.rb:618:in `execute'
from my_path/gems/ruby-2.1.5/gems/selenium-webdriver-2.44.0/lib/selenium/webdriver/remote/bridge.rb:339:in `executeScript'
from my_path/gems/ruby-2.1.5/gems/selenium-webdriver-2.44.0/lib/selenium/webdriver/common/driver.rb:193:in `execute_script'
from my_path/gems/ruby-2.1.5/gems/watir-webdriver-0.6.11/lib/watir-webdriver/atoms.rb:20:in `execute_atom'
from my_path/gems/ruby-2.1.5/gems/watir-webdriver-0.6.11/lib/watir-webdriver/elements/element.rb:373:in `parent'
from t.rb:9:in `<main>'
true
尝试其他网站，得到相同的结果，任何人都知道为什么？感谢