Una buena cuenta regresiva de página JS HTML puede ser precisa para segundos, lo cual es simple, pero práctico
<!doctype html> <html> <head> <meta charset="utf-8"> </head> <body> <DIV id="CountMsg"> <span id="t_d">00 days</span> <span id="t_h">00 hours</span> <span id="t_m">00 minutes</span> <span id="t_s">00 Segundos </span> </div> <script type = "text/javaScript"> function getrtime () {var endtime = new Date ('2014/10/23 10:00:00'); // Fecha límite var NowTime = new Date (); var t = endtime.gettime () - nowtime.gettime (); /*var d = math.floor (t/1000/60/60/24); t- = d*(1000*60*60*24); var h = math.floor (t/1000/60/60); t- = h*60*60*1000; var m = Math.floor (t/1000/60/60); t- = m*60*1000; var s = math.floor (t/1000);*/var d = math.floor (t/1000/60/60/24); var h = Math.floor (T/1000/60/60%24); var m = Math.floor (t/1000/60%60); var s = Math.floor (t/1000%60); document.getElementById ("t_d"). innerhtml = d + "día"; document.getElementById ("t_h"). innerhtml = h + "tiempo"; document.getElementById ("t_m"). innerhtml = m + "minutos"; document.getElementById ("t_s"). innerhtml = s + "segundos"; } setInterval (getrtime, 1000); </script> </body> </html>