js:日期倒计时

 function showTime(){
                var enddate=new Date("2017,6,17");
                var date=new Date();
                var leftdate=enddate.getTime()-date.getTime();
                var time=Math.ceil(leftdate/(24*1000*60*60));//剩下几天
                document.getElementById("dao").innerHTML=time;
//     alert(leftdate);