Start monitoring of node.js

-- This code is a section of nodejs startup.

--The code comments have not been completed, and there are inappropriate comments.

/**
 * Module dependencies.
 */

var app = require('../app');
var debug = require('debug')('untitled:server');
var http = require('http');

/**
 * Get port from environment and store in Express.
 * 80 ports can be modified depending on your needs
 */
var port = normalizePort(process.env.PORT || '80');
app.set('port', port);

/**
 * Create HTTP server.
 */

var server = http.createServer(app);

/**
 * Listen on provided port, on all network interfaces.
 *Turn on listening - you can specify the port number and IP
 *Note here that if the server hosts file does not map 127.0.0.1 and localhost, the following IP may be required, otherwise you know
 *thanks @IPPP
 *As for public network mapping, ngrok tool is recommended
 */
server.listen(port,'127.0.0.1');
console.log("Service started~~~");
//Service error execute onError function
server.on('error', onError);
//Service listening status and its address port information - don't know how to use it yet!
server.on('listening', onListening);

/**
 * Normalize a port into a number, string, or false.
 */

function normalizePort(val) {
  var port = parseInt (val, 10);

  if (isNaN(port)) {
    // named pipe
    return val;
  }

  if (port >= 0) {
    // port number
    return port;
  }

  return false;
}

/**
 * Event listener for HTTP server "error" event.
 */

function onError(error) {
  if (error.syscall !== 'listen') {
    throw error;
  }

  var bind = typeof port === 'string'
    ? 'Pipe ' + port
    : 'Port' + port;

  // handle specific listen errors with friendly messages
  switch (error.code) {
    case 'EACCES':
      console.error(bind + ' requires elevated privileges');
      // process terminated
      process.exit(1);
      break;
    case 'EADDRINUSE':
      console.error(bind + ' is already in use');
      process.exit(1);
      break;
    default:
      throw error;
  }
}

/**
 * Event listener for HTTP server "listening" event.
 */
function onListening() {
  var addr = server.address();
  var bind = typeof addr === 'string'
    ? 'pipe ' + addr
    : 'port ' + addr.port;
  debug('Listening on ' + bind);
  console.log('Listening on ' + bind);
}

 ---------------------------------------------------------------------------------------------------------------------

*、@IPPP

The inspiration for solving the IP problem comes from
https://my.oschina.net/tearlight/blog/195543
great
The problem that has arisen is: if you do not provide hostname, you can only use localhost to access. Later, you can access it in three ways without providing hostname. It is strange to say!