JavaScript 实现指定日期倒计时功能示例

<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <title>倒计时</title>
  </head>
  <body>
    <input type="text" name="time" id="time" value="2017-09-22" />
    <input type="button" name="okbtn" id="okbtn" value="确认" />
    <br />
    <p id="textp">这里显示倒计时</p>
  </body>
<script type="text/javascript">
  var okbtn=document.getElementById("okbtn");
  textp=document.getElementById("textp");
  okbtn.onclick=function(){
    var time=document.getElementById("time");
    var timevalue=time.value;
    //通过正则表达式确认输入格式是否正确
    var patt=/^(\d{1,4})(-)(\d{1,2})\2(\d{1,2})$/;
    if(patt.test(timevalue)==false){
      //如果不正确
      textp.innerHTML="输入格式不满足YYYY-MM-DD";
      return false;
    }else{
      textp.innerHTML="这里显示倒计时";
    }
    //获取输入的年月日
    var timearray=timevalue.split("-");
    //ShowLeftTime(timearray[0],timearray[1],timearray[2]);
    setInterval(function(){ShowLeftTime(timearray[0],timearray[1],timearray[2]);},1000);
  }
  function ShowLeftTime(year,month,date){
        //得出剩余时间
    var now=new Date();
    var endDate=new Date(year,month-1,date);
    var leftTime=endDate.getTime()-now.getTime();
    var leftsecond=parseInt(leftTime/1000);
    var day=Math.floor(leftsecond/(60*60*24));
    var hour=Math.floor((leftsecond-day*24*60*60)/3600);
    var minute=Math.floor((leftsecond-day*24*60*60-hour*3600)/60);
    var second=Math.floor(leftsecond-day*60*60*24-hour*60*60-minute*60);
    //显示剩余时间
    textp.innerHTML="距离"+year+"年"+month+"月"+date+"日"
    +"还有"+day+"天"+hour+"小时"+minute+"分"+second+"秒";
  }
</script>
</html>