recorder.js

var callback = function(mutations, observer) {
	// Checking for falsey mutation value to short-circuit and prevent errors
	// I'm sure there will never be more than one attribute mutation at a time, right? 
	if(!mutations[0] || mutations[0].oldValue !== "display: none;") {
		return;
	}
		
	// Game is now over
	console.log("Recording data!");
	var data = {};
	switch(document.getElementsByClassName("c")[0].textContent) {
		case "Paper.io 2":
			var timeArray = document.getElementsByClassName("da_pt")[0].textContent.split(":");
			data = {
				mode: "paper2_classic",
				kills: parseInt(document.getElementsByClassName("da_pk")[0].textContent),
				score: parseFloat(document.getElementsByClassName("da_sc")[0].textContent),
				time: timeArray[0]*60+parseInt(timeArray[1])
			};
			break;
		default:
			console.log("Tried to record unknown game mode "+document.getElementsByClassName("c")[0].textContent);
	}
	if(data.mode) {
		chrome.runtime.sendMessage(data, function(response) {
			// TODO: add response to add a nice message to the page, eg: "That was a great game!" or "Average score: 11.25%".
			console.log(response);
		});
	}
};

var observer = new MutationObserver(callback);

observer.observe(document.getElementById("game_over"), {attributes: true, attributeOldValue: true});

console.log("Done setting the observer @ "+(new Date).getTime());