Detect multiple tabs of your site

This snippet of code, will detect how many tabs are open and how many are active (visible) and if none of tabs is active, it will choose last opened tab, as active one This code will handle on windows/tab crash too.

by rezaamya

HTML

<html>
<body>
Open in several tabs or windows
<div id="holder_element"></div>
</body>
</html>

JavaScript

//localStorage.clear();
manage_crash();

//Create a windows ID for each windows that is oppened
var current_window_id = Date.now() + "";//convert to string
var time_period = 3000;//ms

//Check to see if PageVisibility API is supported or not
var PV_API = page_visibility_API_check();

/************************
	** PAGE VISIBILITY API **
	*************************/
function page_visibility_API_check ()
{
  var page_visibility_API = false;
  var visibility_change_handler = false;
  if ('hidden' in document)
  {
    page_visibility_API = 'hidden';
    visibility_change_handler = 'visibilitychange';
  }
  else
  {
    var prefixes = ['webkit','moz','ms','o'];
    //loop over all the known prefixes
    for (var i = 0; i < prefixes.length; i++){
      if ((prefixes[i] + 'Hidden') in document)
      {
        page_visibility_API = prefixes[i] + 'Hidden';
        visibility_change_handler = prefixes[i] + 'visibilitychange';
      }
    }
  }

  if (!page_visibility_API)
  {
    //PageVisibility API is not supported in this device
    return page_visibility_API;
  }

  return {"hidden": page_visibility_API, "handler": visibility_change_handler};
}

if (PV_API)
{
  document.addEventListener(PV_API.handler, function(){
    //console.log("current_window_id", current_window_id, "document[PV_API.hidden]", document[PV_API.hidden]);
    if (document[PV_API.hidden])
    {
      //windows is hidden now
      remove_from_active_windows(current_window_id);
      //skip_once = true;
    }
    else
    {
      //windows is visible now
      //add_to_active_windows(current_window_id);
      //skip_once = false;
      check_current_window_status ();
    }
  }, false);
}

/********************************************
	** ADD CURRENT WINDOW TO main_windows LIST **
	*********************************************/
add_to_main_windows_list(current_window_id);
//update active_window to current window
localStorage.active_window =...