Tutorial available here: How to write your own native Node.js extension or in TUTORIAL.md
This is a follow up to How to roll out your own Javascript API with V8.
Using npm:
npm install notify
Manually:
node-waf configure && node-waf build
var notify = require("notify"); // or "../build/default/gtknotify.node" if you build manually
var notification = new notify.notification();
notification.title = "Notification title";
notification.icon = "emblem-default"; // see /usr/share/icons/gnome/16x16
notification.send("Notification message");