Firefox Jetpack which shows a widget on YouTube watch pages

main.js

const widgets = require("widget");

var ytWidgets = {}

function ytEventOccurred(data){
 if(data.event == "load"){
   ytWidgets[data.url] = widgets.Widget({
     label: "YT Button",
     contentURL: "http://www.youtube.com/favicon.ico"
   });
 }else{
   ytWidgets[data.url].destroy();
   delete ytWidgets[data.url];
 }
}

function ytOnAttach(worker) {
 worker.on('message', ytEventOccurred);
}

var pageMod = require("page-mod");
pageMod.PageMod({
 include: "http://www.youtube.com/watch*",
 contentScriptWhen: 'ready',
 contentScript: [
   "postMessage({'url':document.URL,'event':'load'});",
   "window.addEventListener('unload',function(){postMessage({'url':document.URL,'event':'unload'});},false);"
 ],
 onAttach: ytOnAttach
});