index.js

/* eslint-disable no-console */
const http = require("http");
const app = require("./app");

/**
 * Create HTTP server.
 */
const server = http.createServer(app);

/**
 * Normalize a port into a number, string, or false.
 */
const normalizePort = (val) => {
  const numericPort = parseInt(val, 10);

  // eslint-disable-next-line no-restricted-globals
  if (isNaN(numericPort)) {
    // named pipe
    return val;
  }

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

  return false;
};

/**
 * Get port from environment and store in Express.
 */
const port = normalizePort(process.env.PORT || "3000");
app.set("port", port);

/**
 * Event listener for HTTP server "error" event.
 */
const onError = (error) => {
  if (error.syscall !== "listen") {
    throw error;
  }

  const bind = typeof port === "string" ? `Pipe ${port}` : `Port ${port}`;

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

/**
 * Event listener for HTTP server "listening" event.
 */
const onListening = () => {
  const addr = server.address();
  const bind = typeof addr === "string" ? `pipe ${addr}` : `port ${addr.port}`;
  console.log(`Listening on ${bind}`);
};

/**
 * Listen on provided port, on all network interfaces.
 */
server.listen(port);
server.on("error", onError);
server.on("listening", onListening);