<script type="text/javascript">
    var date = new Date();
    var seperator1 = "-";
    var seperator2 = ":";
    var year = date.getFullYear();
    var month = date.getMonth() + 1;
    var hour = date.getHours();
    var minutes = date.getMinutes();
    var strDate = date.getDate();
    if (month >= 1 && month <= 9) {
        month = "0" + month;
    }
    if (strDate >= 0 && strDate <= 9) {
        strDate = "0" + strDate;
    }
    if (hour >= 0 && hour <= 9) {
    hour = "0" + hour;
    }
    if (minutes >= 0 && minutes <= 9) {
    minutes = "0" + minutes;
    }
    var currentdate = year + seperator1 + month + seperator1 + strDate
            + " " + hour + seperator2 + minutes;
    var currentTime = parseInt(currentdate.replace(/-/g,"").replace(/\s/g,"").replace(/(:)/g,""));
    var targetTime = parseInt($("#date").html().replace(/-/g,"").replace(/\s/g,"").replace(/(:)/g,""));
    var time = (currentTime-targetTime)>20000;
    alert(time);
    if(time){
  alert("if執行");
  $("#ifRead").replaceWith("<span>已讀</span>");
  alert("已讀");
    }
  </script>