Find a free port in Node.js

free-port.js

/*
  Much better approach than trying to connect to a range of ports.
*/

var net = require('net');

getFreePort(function(err, port) {
  if (err) throw err;

  console.log('Port: ' + port);
});

function getFreePort(fn) {
  var server = net.createServer();
  var calledFn = false;

  server.on('error', function(err) {
    server.close();

    if (!calledFn) {
      calledFn = true;
      fn(err);
    }
  });

  server.listen(0, function() {
    var port = server.address().port;

    server.close();

    if (!calledFn) {
      calledFn = true;

      if (!port) {
        fn(new Error('Unable to get the server\'s given port'));
      } else {
        fn(null, port);
      }
    }
  });
}