Node.js res.send is not a function

Swap req & res : function(req, res)

You've got the res and req parameters the wrong way around.

app.get('/', function(res, req)

should be

app.get('/', function(req, res)

Source: API docs.

According to the API reference, the first param always contain request req, then response res.

So change first param res to req:

app.get('/', function(req, res) {
    res.send("Rendering file")
}

It should fix it.