How to set index.php and not index.html with nodejs server

i want to modify my index.html to index.php. How to do this?

My application is all with nodejs and my index is HTML format, but I need use PHP format.

Check my route:

app.get('/', function (req, res) {
  res.render("../public/index"); //before index.html now index.php
});

I try add the formart .php and does not work.

via SMM