Firefox test add-on, trying to find the simplest way to monitor loading of pages in tabs

bootstrap.js

"use strict";

// exploring add-ons API
// Goal: monitor all tabs, run code when new page loads
// Optionally also listen for document mutations

// some standard vars / shortcuts into Gecko's internals: classes, interfaces, utils
const Cc = Components.classes;
const Ci = Components.interfaces;
const Cu = Components.utils;

// I want to have console.log() around, here's some code for that
var aConsoleService = Cc["@mozilla.org/consoleservice;1"].getService(Ci.nsIConsoleService);
var console = {log:function(str){aConsoleService.logStringMessage(str);}}

// eventually we would like this method to run each time a page loads inside a tab
function tab_onLoad(evt){
    console.log('TAB DOMContentLoaded!')
    console.log(evt.type + ' on ' + evt.target.wrappedJSObject + ' (currentTarget : ' + evt.currentTarget+ ')');
    // we need only one event per navigation, let's remove the listener again
    evt.target.removeEventListener('DOMContentLoaded', tab_onLoad, false);
    // manipulate document here.. presumably
}
// seems we have to attach something to every new window to start monitoring its tabs..
function win_onLoad(evt){
    // adding tab progress listener in the new window
    try{
        this.gBrowser.addTabsProgressListener(tabProgressListener);
    }catch(e){
        console.log('this.gBrowser failed')
        console.log(e);
    }
}

var windowListener = {
  onOpenWindow: function(aWindow) {
    console.log('onOpenWindow ' + aWindow);
    /*for(var prop in aWindow){ // explore the API manually..
        console.log(prop);
    }*/
    // Wait for the window to finish loading
    // some page on the internet says gBrowser might not be usable unless we do this..
    let domWindow = aWindow.QueryInterface(Ci.nsIInterfaceRequestor).getInterface(Ci.nsIDOMWindowInternal || Ci.nsIDOMWindow);
    domWindow.addEventListener("load", win_onLoad, false);
  },

  onCloseWindow: function(aWindow) {
    // Do we have to clean up to avoid memory leaks? Or will the GC handle it all when the window is gone?
    let domWindow = aWindow.QueryInterface(Ci.nsIInterfaceRequestor).getInterface(Ci.nsIDOMWindowInternal || Ci.nsIDOMWindow);
    domWindow.removeEventListener("load", win_onLoad, false);
    // If we need to clean up, we probably have to kill the progress listener too. This doesn't seem to work though:
    // domWindow.gBrowser.removeTabsProgressListener(tabProgressListener);
  },
  onWindowTitleChange: function(aWindow, aTitle) {}
};

// To listen for the actual load event, we first detect location change events and attach load listener from there
var tabProgressListener = { onLocationChange:function(aBrowser, aWebProgress, aRequest, aLocation, aFlags){
    if(aBrowser && aRequest){
        if(aBrowser.getAttribute('type') === 'content-primary'){
            aBrowser.contentWindow.addEventListener('DOMContentLoaded', tab_onLoad, false);
        }
    }

}, onProgressChange: function(aBrowser, aWebProgress, aRequest, aCurSelfProgress, aMaxSelfProgress, aCurTotalProgress, aMaxTotalProgress){} };
tabProgressListener.onSecurityChange = tabProgressListener.onStateChange = tabProgressListener.onStatusChange = tabProgressListener.onRefreshAttempted = tabProgressListener.onLinkIconAvailable = function(){}

function startup(aData, aReason) { console.log('startup ' + aData + ', ' + aReason);
  // enumerate existing windows and add tab progress listener
  let wm = Cc["@mozilla.org/appshell/window-mediator;1"].getService(Ci.nsIWindowMediator);
  let windows = wm.getEnumerator("navigator:browser");
  while (windows.hasMoreElements()) {
    let domWindow = windows.getNext().QueryInterface(Ci.nsIDOMWindow);
    domWindow.gBrowser.addTabsProgressListener(tabProgressListener);
  }

  // Load into any new windows
  wm.addListener(windowListener);
}

function shutdown(aData, aReason) {
  // When the application is shutting down we normally don't have to clean
  // up any UI changes made
  console.log('shutdown ' + aData + ' , ' + aReason);
  if (aReason == APP_SHUTDOWN)
    return;

  let wm = Cc["@mozilla.org/appshell/window-mediator;1"].getService(Ci.nsIWindowMediator);
  // Stop listening for new windows
  wm.removeListener(windowListener);

  // Unload from any existing windows
  let windows = wm.getEnumerator("navigator:browser");
  while (windows.hasMoreElements()) {
    let domWindow = windows.getNext().QueryInterface(Ci.nsIDOMWindow);
    domWindow.removeEventListener("load", onLoad, false);
  }
// TODO: we have more events to remove, how?
}

function install(aData, aReason) {} function uninstall(aData, aReason) {}