javascript - asp.net (VB) countdown timer that is persistent through postbacks -

i have button , label on asp.net vb page , when button pressed need countdown timer begin 10 mins , update every seconds, 09:59, 09:58, 09:57 etc.... need timer continue countdown despite postbacks or temporarily redirecting different page.

so far have tried using asp.net timers (with async triggers/update panels) seconds countdown needs 1 second postback , going quite resource expensive when there hundreds of users accessing system. writes exact countdown time session variable retrieved when page reloaded - ugly method way can work.

update - have found solution problem:

using great javascript countdown script http://scripts.hashemian.com/js/countdown.js

aspx page:

<asp:literal runat="server" id="jstimemarker"/>       <script type="text/javascript" src="http://scripts.hashemian.com/js/countdown.jss"></script>     <asp:button runat="server" text="10 mins" id="btn10mins"/> 

code behind page:

sub page_load(sender object, e eventargs) handles me.load     if not ispostback         ' set countdown timer based on if cookie set         if not request.cookies("countdowntimer") nothing             timemarkerrender(request.cookies("countdowntimer")("data"))         end if     end if end sub  sub timemarkerrender(targetdatetime string)     dim sb stringbuilder = new stringbuilder()     sb.append("<script type=""text/javascript"">")     'sb.append("targetdate = ""08/28/2013 18:11:29"";")     sb.append("targetdate = " & "'" & targetdatetime & "'" & ";")     sb.append("countactive = true;")     sb.append("countstepper = -1;")     sb.append("leadingzero = true;")     sb.append("displayformat = ""%%m%%:%%s%%"";")     sb.append("finishmessage = ""finished"";")     sb.append("</script> ")     jstimemarker.text = sb.tostring() end sub  protected sub btn10mins_click(sender object, e eventargs) handles btn10mins.click     response.cookies("countdowntimer")("data") = now.addminutes(10).tostring("mm/dd/yyyy hh:mm:ss")     response.redirect(request.rawurl) end sub 

i mean basic problem, you've discovered, persisting though sort of postback going difficult , not accurate. can either use iframe content page , have counter running in javascript on outside page or can launch new window counter running while user working?

here simple countdown timer in javascript: https://mindgrader.com/tutorials/1-how-to-create-a-simple-javascript-countdown-timer