app.js

var YUI = require('yui').YUI,
    Y   = YUI();

Y.use('parallel');

require('./second');

output.txt

$ node app.js          
Type of Y.Handlebars: undefined

second.js

var Y = require('yui/handlebars');

console.log('Type of Y.Handlebars: ' + typeof Y.Handlebars );