Playground.js is a framework for your javascript based games. It gives you out-of-box access to essentials like mouse, keyboard, sound and well designed architecture that you can expand to your needs.
var tween = this.tween(...);
/* fired every time the event occurs for this tween */
tween.on
/* fired once then removed */
tween.once
tween.on("finished", function() { }, context);
tween.on("loop", function() { }, context);
/* context is optional - it replaces `this` within callback */