doorbell.js

var gpio = require("gpio");
var net = require('net');

var host = '192.168.1.101';
var port = 5000;
var client = false;
var canRing = true;


var gpio4 = gpio.export(4, {
  direction: 'in',

  interval: 200,

  ready: function() {
    console.log("Initialized gpio pin4.")
    net.createServer(function (sock) {
      console.log('Client connected!');
      client = sock;
      if (canRing == false) {
        // should practically never happen, but whatever:
        alertClient();
      }
    }).listen(port, host);
    console.log('Server listening...');
  }
});

gpio4.on("change", function(val) {
  if (0 == val) {
    // pin 4 connected to ground:
    onDoorbellPress();
  }
});

function alertClient() {
  console.log('Alerting client...');
  client.write('RINGRING\n');
  client.on('data', function(data) {
    console.log('Received OK message. Closing connection.');
    sock.destroy();
  });
  client.on('error', function (err) {
    console.log('Error alerting client ' + client + ':' + err);
    client = false;
  });
  console.log('Message sent.');
}

function onDoorbellPress() {
    if (canRing) {
  canRing = false;
  console.log("RINGRING");
  // prevent multiple alerts within the same second:
  setTimeout(function onTimer() {
      canRing = true;
    }, 1000);
      if (client) {
        alertClient();
      } else {
        console.log('No client connected.');
      }
  }
}