var socket = io.connect();

socket.on('connect', function () {
  alert('Socket is connected.');
});

socket.on('disconnect', function () {
  alert('Socket is disconnected.');
});

var socket = io.connect('http://<ip>:<port>', {
    reconnection: false
});
socket.on('connect_error', function() {
    console.log('Failed to connect to server');
});

var socket;
try {
    socket = io();
}
catch() {
    window.location = "nodeServerDown.php";
}