gistfile1.js

YUI().use('event', 'io', 'nodejs-dom', function(Y) {
    //Do your stuff

    //Inside the request handler callback:
    //Now each request get's a new DOM and not a shared one.
    Y.use('nodejs-dom', function(Y) {
        var document = Y.Browser.document;
        document.createElement('div');
    });
});