Basic server Heroku

index.js

var express = require('express');
var app = express();

app.get('/', function (req, res) {
    res.send('Hola Luis!');
});

app.listen(process.env.PORT || 3000, function () {
    console.log('App listening on port 3000!');
})

package.json

{
  "name": "luis-test",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1",
    "start": "node index.js"
  },
  "author": "",
  "license": "ISC",
  "dependencies": {
    "express": "^4.13.3"    
  }
}