js倒计时

<div class="nlpz_sjdjs">剩余：<span>00</span>:<span>00</span>:<span>00</span></div>

<script type="text/javascript">
    var starttime = new Date("2018-03-09 15:44:00");
    function tt(){
        var nowtime = new Date();
        //alert(nowtime);
        var time = starttime - nowtime;
        var day = parseInt(time / 1000 / 60 / 60 / 24);//天
        var hour = parseInt(time / 1000 / 60 / 60 % 24);//小时
        var minute = parseInt(time / 1000 / 60 % 60);//分钟
        var seconds = parseInt(time / 1000 % 60);//秒
        
        if(hour<=0 && minute<=0 && seconds<=0){
            clearInterval(sj);
            $('.nlpz_sjdjs').html("活动已结束");
        }else{
            $('.nlpz_sjdjs').html('剩余'+day+'天:'+'<span>'+hour+'</span>'+':'+'<span>'+minute+'</span>'+':'+'<span>'+seconds+'</span>');
        } 
    }
    var sj = setInterval(function () {tt();}, 1000);
</script>

注意引入jquery