native.rb

require 'native'

doc = Native(`document`)
puts %Q[Object instance of #{doc.body.class} for "#{doc.title}"]
puts %Q[Body DOM element class: "#{doc.body.className}"]

# => Object instance of Native::Object for "Try Opal: Browser compiler and REPL"
# => Body DOM element class: "try try_index"

wrapped.rb

require 'native'

class Body
  include Native

  alias_native :class_name, :className
end

class Document
  include Native

  alias_native :title
  alias_native :body, :body, as: Body
end

doc = Document.new(`document`)
puts %Q[Object instance of #{doc.body.class} for "#{doc.title}"]
puts %Q[Body DOM element class: "#{doc.body.class_name}"]

# => Object instance of Body for "Try Opal: Browser compiler and REPL"
# => Body DOM element class: "try try_index"