为什么我这段代码执行出来时间是负的，新人小白初学求大神指导

function showTime() {
var currentDate = new Date();
var startDate = new Date(2016, 07, 22);
var date3 = currentDate-startDate;
var days=Math.floor(date3/(24*3600*1000));
var leave1=date3%(24*3600*1000); //计算天数后剩余的毫秒数
var hours=Math.floor(leave1/(3600*1000));
var leave2=leave1%(3600*1000); //计算小时数后剩余的毫秒数
var minutes=Math.floor(leave2/(60*1000));
var leave3=leave2%(60*1000); //计算分钟数后剩余的毫秒数
var seconds=Math.round(leave3/1000);
if (minutes < 10)
minutes = "0" + minutes;
if (seconds < 10)
seconds = "0" + seconds;
var currentTimeString = "Dear Nicole:<br>"
+ "I have been in love with you for:<br> "
+ "&nbsp&nbsp&nbsp&nbsp&nbsp"
+ "<c style=\"color: #CCFF99; text-shadow:2px 3px 3px #222; font-family:Microsoft YaHei; font-size:24px\" >" + days +" </c>day "
+ "<c style=\"color: #CCFF99; text-shadow:2px 3px 3px #222; font-family:Microsoft YaHei; font-size:24px\" >" + hours+" </c>hour "
+"<c style=\"color: #CCFF99; text-shadow:2px 3px 3px #222; font-family:Microsoft YaHei; font-size:24px\" >" + minutes+" </c>min "
+"<c style=\"color: #CCFF99; text-shadow:2px 3px 3px #222; font-family:Microsoft YaHei; font-size:24px\" >" +seconds+" </c>sec<br>"
+ "&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp只愿执子之手,与子偕老.<br>"
+ "&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp"
+"<c style=\"color: #CCCCCC; text-shadow:2px 3px 3px #222; font-family:Microsoft YaHei; font-size:20px\" >----51bbw.cn 2014-01-01</c>";
document.getElementById("show").innerHTML=currentTimeString; //改这地方
window.setTimeout("showTime()", 1000);
}