env.rb

require 'v8'

cxt = V8::Context.new
cxt.load('env.js')

cxt['document'].tap do |document|
  puts document
  document.createElement('div').tap do |div|
    puts div
    div.setAttribute("id", "foo")
    puts div.getAttribute("id")
    document.documentElement.appendChild(div)
    puts document.childNodes.length
    puts document.childNodes[0]
  end
end

env.rb.out

[object HTMLDocument]
[object HTMLDivElement]
foo
1
[object HTMLHtmlElement]
Program exited with code #0 after 0.22 seconds.