Answers for "res.send is not a function"

req.sendFile is not a function

var express = require('express');
 var app = express();
 app.get('/', function(req, res) {
     res.sendFile('path-to-file');
 });
 app.listen(PORT);

res.send is not a function

You need to do res.end instead of res.send. 
res.send is a part of express module and not of core http module.