Gently launch clients one after another, against a simple server.

clients.js

var Socket = require('engine.io-client').Socket;
var count = 0;
var opened = 0;
var MAX = 10;

initClient();

function initClient() {
	var conn = new Socket({
		host: 'localhost'
	,	port: 8007
	});
	conn.on('error', function(e) {
		console.log(e);
	});
	conn.on('open', function() {
	console.log('opened', opened++);
	if (opened <= MAX) process.nextTick(initClient);
	conn.on('message', function() {
		console.log('received', count++);
	});
	conn.on('close', function(e) {
		console.log('close', e);
	});
	});
}

result.log

dev:~/tmp/wstests$ node test.js 
opened 0
opened 1
received 0
received 1
opened 2
opened 3
received 2
opened 4
received 3
opened 5
opened 6
opened 7
received 4
received 5
dev:~/tmp/wstests$ 

server.js

var engine = require('engine.io')
  , server = engine.listen(8007)

server.on('connection', function (socket) {
  socket.send('utf 8 string');
});