用JS计算两个日期之间有多少个休息日

<script type="text/javascript">
function weekendBetween(dtStart, dtEnd) {   
    if (typeof dtEnd == 'string' ) 
        dtEnd = StringToDate(dtEnd); 
    if (typeof dtStart == 'string' ) 
        dtStart = StringToDate(dtStart); 

    var days =  parseInt((dtEnd - dtStart) / 86400000); 
    var adds = 0;
    var m = (days+ dtStart.getDay() +1) % 7;
    if(m > 0)
        adds = m;
    if(m >2)
        adds = 2;
   
    var redu = 0
    if(dtStart.getDay() > 0)
        redu = 2;
    if(dtStart.getDay() ==1)
        redu =1;
       
    var subtotal = parseInt((days + dtStart.getDay() +1)/7)*2;
    return subtotal - redu + adds;
}
  function StringToDate(DateStr) 
{ 
    var converted = Date.parse(DateStr); 
    var myDate = new Date(converted); 
    if (isNaN(myDate)) 
    { 
        var arys= DateStr.split('-'); 
        myDate = new Date(arys[0],arys[1],arys[2]); 
    } 
    return myDate; 
}


alert("2-1~~~~2-18");
alert(weekendBetween(new Date(2008,2,1), new Date(2008,2,18)));

alert("2-1~~~~2-15,  字符型参数");
alert(weekendBetween("2008-2-1","2008-2-15"));

alert("2-1~~~~2-16,  字符型参数");
alert(weekendBetween("2008-2-1","2008-2-16"));

alert("2-1~~~~2-17,  字符型参数");
alert(weekendBetween("2008-2-1","2008-2-17"));

alert("2-3~~~~2-16,  字符型参数");
alert(weekendBetween("2008-2-3","2008-2-16"));
</script>