javascript - Countdown don't stay run if close tabs -

i'm learning make countdown, , find guide on internet. when page closed countdown stops , if open page again countdown runs again, want make countdown continues run if page closed http://jsfiddle.net/fnsy4/

function setcookie(cname,cvalue,exdays)  {  var d = new date();  d.settime(d.gettime()+(exdays*24*60*60*1000));  var expires = "expires="+d.togmtstring();  document.cookie = cname + "=" + cvalue + "; " + expires;  }  function getcookie(cname)  {  var name = cname + "=";  var ca = document.cookie.split(';');  for(var i=0; i<ca.length; i++)     {    var c = ca[i].trim();    if (c.indexof(name)==0) return c.substring(name.length,c.length);    }  return "";  }    //check existing cookie  cook=getcookie("my_cookie");    if(cook==""){     //cookie not found, set seconds=60     var seconds = 60;  }else{       seconds = cook;       console.log(cook);  }    function secondpassed() {      var minutes = math.round((seconds - 30)/60);      var remainingseconds = seconds % 60;      if (remainingseconds < 10) {          remainingseconds = "0" + remainingseconds;       }      //store seconds cookie      setcookie("my_cookie",seconds,5); //here 5 expiry days            document.getelementbyid('countdown').innerhtml = minutes + ":" +    remainingseconds;      if (seconds == 0) {          clearinterval(countdowntimer);          document.getelementbyid('countdown').innerhtml = "buzz buzz";      } else {              seconds--;      }  }    var countdowntimer = setinterval(secondpassed, 1000);

<span id="countdown" class="timer"></span>

if want countdown effective if tab closed, you'll have reconsider 2 (or more) options:

• you server side , countdown displayed in client window processed in server
• you set countdown given date (let's say) 16/12/2014 11:00:00 make calculus display. given date constant, no matter how many times countdown closed/opened, it'll true.
• once start countdown, save ending datetime cookie , restore countdown next time open page.