js倒计时

<script type="text/javascript">

                $(function(){
                    countTime();
                })

                function countTime(){
                    //获取当前时间
                    var date = new Date();
                    var now = date.getTime();

                    //设置截止时间
                    var str = "2018/04/18 22:05:08";
                    var endDate = new Date(str);
                    var end = endDate.getTime();

                    //时间差
                    var leftTime = end - now;

                    //定义变量 d,h,m,s保存倒计时的时间
                    var d,h,m,s;
                    if (leftTime>=0) {
                        d = Math.floor(leftTime/1000/60/60/24);
                        h = Math.floor(leftTime/1000/60/60%24);
                        m = Math.floor(leftTime/1000/60%60);
                        s = Math.floor(leftTime/1000%60);
                    }
                    var timeout = "付款倒计时:  "+checkTime(h)+":"+checkTime(m)+":"+checkTime(s);
                    $("#timebox").html(timeout);
                    //递归每秒调用countTime方法，显示动态时间效果
                    setTimeout(countTime,1000);
                }

                //小于10补零
                function checkTime(i) {
                    if (i<10) {
                        i = "0" +i;
                    }
                    return i;
                };
            </script>

运行效果如下：