gistfile1.js

function Ball(colour) {
	// ...
}
Ball.prototype.on = function(eventName, callback) {
	glow.events.addListener(this, eventName, callback);
};
Ball.prototype._moved = function() {
	if (this._directionChange) {
		glow.events.fire(this, 'bounce');
	}
};

// usage:

var redBall = new Ball('#f00');

redBall.on('bounce', function() {
	console.log('Red ball bounced');
});