AJAX update panel, pass information to JavaScript

Question

I'm having a countdown timer like these

var leave =<%=seconds %>;
CounterTimer();
var interv=setInterval("CounterTimer()",1000);
function CounterTimer() {
try {
   if (leave>0)
    {
        var day = Math.floor(leave / ( 60 * 60 * 24))
        var hour = Math.floor(leave / 3600) - (day * 24)
        var minute = Math.floor(leave / 60) - (day * 24 *60) - (hour * 60)
        var second = Math.floor(leave) - (day * 24 *60*60) - (hour * 60 * 60) - (minute*60)
        hour=hour<10 ? "0" + hour : hour;
        minute=minute<10 ? "0" + minute : minute;
        second=second<10 ? "0" + second : second;
        var remain=day + " days   "+hour + ":"+minute+":"+second;
        leave = leave - 1;
        document.getElementById("<%=lblRemain.ClientID %>").innerText=remain;
    }
    else
    {
        try{
            document.getElementById("<%=lblRemain.ClientID %>").innerText="Auction closed";}
            catch(err) {   //alert(err.Message);
            }
    }
    }
    catch(err)
    { alert(err.Message);}

}

And I'm setting/putting the value of the leave variable from c#

seconds = (ClosingOn - DateTime.Now).TotalSeconds;

On the webpage I have a UpdatePanel showing auction information and this UpdatePanel is updated every 5 second. During the countdown I would like to be able to change the remaining time in the timer event

protected void Timer1_Tick(object sender, EventArgs e)
{
    ClosingOn.AddMinutes(5);
    seconds = (ClosingOn - DateTime.Now).TotalSeconds;
}

But this change doesn't affect the leave variable in the JavaScript :(

Can you see a way out of this?

I'm on a very slow interent connection so having a updatepanel updating every second is not an option.

Answer 1

That's because this expression var leave =<%=seconds %>; evaluated only once, actually on page rendering. Instead of evaluating leave value with <%= seconds %> expression, add HiddenField into UpdatePanel where Timer control placed. In javascript you can get this field's value and parse it to int. And in Timer1_Tick you can assign on that hidden field new value.

Or if you looking for a quick workaround you can add at the end of Timer1_Tick method following code:

ScriptManager.RegisterStartupScript(Timer1, typeof(Timer), Guid.NewGuid().ToString(), string.Format("leave = {0}", seconds), true);