js 获取当前时间并计算与10月1日倒计时

html代码如下:

<input type="text" id="year" value="2018-10-1" />
<button type="button" id="but">倒计时</button>
<input type="text" id="time" value="" readonly="readonly"/>

js代码如下:

document.getElementById("but").onclick=function(){
    var timer=setInterval(function(){
        var _year=document.getElementById("year").value;
         _year=Date.parse(_year);
          var _now=Date.now();
          var _diff=_year- _now;
          var totalSeconds=Math.ceil(_diff/1000);
        var seconds= totalSeconds%60,
            minutes=Math.floor(totalSeconds/60),
            hours=Math.floor(totalSeconds/(60*60)%24,
            days=Math.floor(totalSeconds/(24*60*60)));
    document.getElementById("time").value=days+"天"+hours+"时"+minutes+"分"+seconds+"秒";
    },1000);    
    }