Question

I am making a Firefox add-on that will log how long the user keeps a webpage open in his browser.

I was able to catch the link of every new webpage opening in the browser (both in new tab or in already opened one) by adding a progress listener:

addProgressListener(myAddon_urlBarListener,
                    Components.interfaces.nsIWebProgress.NOTIFY_ALL);

Then I use onLocationChange to get the new URL for a tab.

The problem is that I don’t know the old URL for the tab to be able to stop the timer and to calculate the duration for that webpage. Right now I am only able to calculate time if I close the tab of the webpage because I am able to catch closing tab event and what is the link in the page before closing.

I need a way to catch the URL of old webpage if I open an new URL in the same tab, and this needs to work even if more that one tab is opened in the browser. Btw, I am not working with jQuery but if it is required I will.

Answer 1

What if the same URL is opened in two tabs? You should be focusing on tabs, not URLs. Your onLocationChange function should find the <browser> element associated with the tab and just remember its URL (as long as the time). Next time you see the same <browser> element you will have all the information you need. Best way to store data about the browser is currently WeakMap, and finding the <browser> element is possible using tabbrowser.getBrowserForDocument() method. So something like this should work:

browsers: new WeakMap(),

onLocationChanged: function(webProgress, request, location, flags)
{
  if (typeof flags == "number" &&
      (flags & Components.interfaces.nsWebProgressListener.LOCATION_CHANGE_SAME_DOCUMENT))
  {
    // Ignore anchor changes
    return;
  }

  var doc = webProgress.DOMWindow.document;
  var browser = gBrowser.getBrowserForDocument(doc);
  if (this.browsers.has(browser))
  {
    // We know this tab already, record data for previous URL
    var data = this.browsers.get(browser);
    recordPageClosed(data.url, data.startTime);
  }

  // Start timer for this tab
  this.browsers.set(browser, {url: location.spec, startTime: Date.now()});
}

Of course you will still have to handle TabClose event. There you will need tabbrowser.getBrowserForTab() method to find the <browser> element by its corresponding <tab> element.