How to serve frontend and backoffice with a NodeJS application on Heroku?

I am using Nodejs with AngularJS for my backoffice application.

It stays on

http://localhost:3000/#!/

But what I need is, this url points to my frontend, and a subdomain like

http://backoffice.localhost:3000/#!/ 

opens my backoffice.

I tried some nodejs libraries like subomain, but I couldn't target the static files.

What is the best approach?