<!DOCTYPE HTML>
<html>
<head>
    <?php
    $str = 'Tue Dec 15 2016';
    $timestamp = strtotime($str); ?>
</head>
<body>
<span id="counter12"></span>
<script>
    // self executing function here
    (function () {
        var seconds =<?=json_encode($timestamp);?>;
        var interval = setInterval(runFunction, 1000);

        var spCounter = document.getElementById("counter12");
        function runFunction() {
            spCounter.innerHTML = "Kalan Süre: " + --seconds;
            if (seconds == 0)
                clearInterval(interval);
        }
    })();
</script>
</body>
</html>