HTML:

<div class="countdown">
Geri Sayım!
<span id="clock"></span>
</div>
JS:

$('#clock').countdown('2020/10/10 12:34:56')
.on('update.countdown', function(event) {
var format = '%H:%M:%S';
if(event.offset.totalDays > 0) {
format = '%-d day%!d ' + format;
}
if(event.offset.weeks > 0) {
format = '%-w week%!w ' + format;
}
$(this).html(event.strftime(format));
})
.on('finish.countdown', function(event) {
$(this).html('Geri sayım tamamlandı!')
.parent().addClass('disabled');

});