倒計時：計算時間差

var newTime = new Date().getTime();
var oldTime = new Date().getTime();
//相差的毫秒數
var syhm =  newTime - oldTime;
var h = Math.floor(syhm%(24*60*60*1000)/(60*60*1000))
var m = Math.floor(syhm%(24*60*60*1000)%(60*60*1000)/(60*1000));
var s = Math.floor(syhm%(24*60*60*1000)%(60*60*1000)%(60*1000)/1000);
                    
h = h<10 ? '0'+h : h;
m = m<10 ? '0'+m : m;
s = s<10 ? '0'+s : s;