Node.js server.address().address returns ::

Question

If I remember correctly it used to display "localhost" a few days ago. I am not sure what had changed that made server.address().address return double colons (::) instead. I read here that it returns an IPv6 address (::) if it is available but it's disabled on my PC. https://nodejs.org/api/http.html#http_server_listen_port_hostname_backlog_callback

Answer 1

As the docs say,

Begin accepting connections on the specified port and hostname. If the hostname is omitted, the server will accept connections on any IPv6 address (::) when IPv6 is available, or any IPv4 address (0.0.0.0) otherwise. A port value of zero will assign a random port.

So, the following code would print running at http://:::3456:

var express      = require('express');
var app          = express();
var server = app.listen(3456, function () {
    var host = server.address().address;
    var port = server.address().port;
    console.log('running at http://' + host + ':' + port)
});

But if you add an explicit hostname:

var server = app.listen(3456, "127.0.0.1", function () {

It would print what you want to see: running at http://127.0.0.1:3456

Also you might want to use some IP lib as pointed in this answer

Best regards, Alexander

Answer 2

The reason why its choosing IPV6 address is possibly because some other process is using IPV4 port no 3456. This happens sometimes due to automatic updates where new processes are installed.