星期天是0 如何改成7

星期天是0 怎么改成7
   
    <script>
function   a(){
var   curdate=new   Date();
document.all.dn_date.value=curdate.getFullYear()+ "- "+(curdate.getMonth()+1)+ "- "+curdate.getDate();
document.all.dn_week.value=curdate.getDay();
}
function   b(){
var   dateStr=document.all.dn_date.value
var   dateArr=dateStr.split( "- ");
var   nextDate=new   Date(dateArr[0],dateArr[1]-1,dateArr[2]);
document.all.dn_date.value=nextDate.getFullYear()+ "- "+(nextDate.getMonth()+1)+ "- "+nextDate.getDate();
document.all.dn_week.value=nextDate.getDay();
}
function   c(){
var   dateStr=document.all.dn_date.value;
var   dateArr=dateStr.split( "- ");
var   nextDate=new   Date(dateArr[0],dateArr[1],dateArr[2]);
document.all.dn_date.value=nextDate.getFullYear()+ "- "+(nextDate.getMonth()+1)+ "- "+nextDate.getDate();
document.all.dn_week.value=nextDate.getDay();
}
</script>
<input   name= "dn_date "   onfocus= "calendar() "   width= "100 "     value= " <%=date()%> "     size= "10 "     onchange= "c() "/>
  <input   type= "text "     size=10   name= "dn_week "   onclick= "b() ">  
代码如上
现在选择一个日期   比如应该是星期天的话   dn_week里显示的是0
  请帮忙   谢谢

[解决办法]
function b(){
var dateStr=document.all.dn_date.value
var dateArr=dateStr.split( "- ");
var nextDate=new Date(dateArr[0],dateArr[1]-1,dateArr[2]);
document.all.dn_date.value=nextDate.getFullYear()+ "- "+(nextDate.getMonth()+1)+ "- "+nextDate.getDate();
document.all.dn_week.value=nextDate.getDay()==0?7:nextDate.getDay();
}