Can someone explain to me how are they using all JS (node incl server-side rendering) stack in a company that is known for using PHP on the backend ?

Do they have a specific PHP-to-Node bridge on the server side? If they write isomorphic code, either they are writing apps completely separate from PHP or they have some kind of integration (Node-in-PHP?) running?

I would be grateful for hints, I'm looking into working more with FB tech but I can't do Node on the server right now. Knowing how their architecture looks like with PHP/Hack on the backend would really help.