For use with Google's Doubleclick for Publishers (DFP). Taps into dfp's logger function and triggers events.

googletag.on(events,data,callback);

• events - string containing a list of events to bind to.
• data - (optional) data to be passed to the callback upon triggering, passed via arguments[0].data a la jQuery.
• callback - function to be called upon one of the events occuring.

googletag.off(events,callback);

• events - string containing a list of events to remove callbacks from.
• callback - (optional) specific callback function to be removed from googletag.

• gpt-google_js_loaded
• gpt-gpt_fetch
• gpt-gpt_fetched
• gpt-page_load_complete
• gpt-queue_start
• gpt-service_add_slot
• gpt-service_add_targeting
• gpt-service_collapse_containers_enable
• gpt-service_create
• gpt-service_single_request_mode_enable
• gpt-slot_create
• gpt-slot_add_targeting
• gpt-slot_fill
• gpt-slot_fetch
• gpt-slot_receiving
• gpt-slot_render_delay
• gpt-slot_rendering
• gpt-slot_rendered

Notice I use jQuery to cause changes to the DOM but not to bind or unbind the callbacks to the googletag object.

googletag.on("gpt-slot_rendered",function(e,level,message,service,slot,reference){
	var slotId = slot.getSlotId();
	var $slot = $("#"+slotId.getDomId());
	
	if($slot.find("iframe:not([id*=hidden])").map(function(){return this.contentWindow.document;}).find("body").children().length == 0)
		$slot.addClass("empty");
});

googletag.off("gpt-slot_rendered");