How do I store data to be used for all the clients in my server? (like the messages of a chat)
The server that node.js allows you to build, is an application server, which means that state is preserved, between request, on the server side. The following snippet demonstrates this:
var sys = require('sys'),
http = require('http');
var number = 0;
http.createServer(function (req, res) {
console.log(req.method, req.url);
res.writeHead(200, {'Content-Type': 'text/html'});
res.write('<h1>Number is: ' + number + '</h1>');
res.end();
number++;
}).listen(8000);
sys.puts('Server running at http://127.0.0.1:8000/');