A handy function that normalizes a port into a number, string, or false.
npm install --save normalize-port
const http = require('http');
const normalizePort = require('normalize-port');
const port = normalizePort(process.env.PORT || '3000');
const server = http.createServer(listenerOrApp).listen(port, () => {
console.log(`listening on ${port}`)
})
I just pulled this little function out of the default express-generator template.