#Get the first link (or any element you want)
element = browser.div(:id => 'topnavTut').link
 
#Check element's initial target attribute
puts element.attribute_value('target')
#=> "_top"
 
#Execute javascript to change the attribute
script = "return arguments[0].target = 'foo'"
browser.execute_script(script, element) 
 
#Check that the target attribute has changed
puts element.attribute_value('target')
#=> "foo"