child.jade

doctype html
html
  head
    meta(charset='utf-8')
  body
    h1 child!!
    script(src='index.js', type='text/javascript')

index.coffee

href1 = if parent != window then document.referrer else document.location.href

try
  href2 = parent.location.href
catch err
  href2 = document.referrer

console.log href1, href2
# => localhost, localhost

parent.jade

doctype html
html
  head
    meta(charset='utf-8')
    title iframe
    link(href='index.css', rel='stylesheet', type='text/css')
  body
    h1 iframe
    iframe(src='http://***.ngrok.com/child.html')