I'm new to JS and JQ, I have written some code for an ASP .NET form. 

there is one text field called txtJoinDate and other one text field called Expire Date. 

I implemented datepicker for the txtJoinDate and I displayed the picked date on the txtExpireDate. 

I need to make a calculation so that the expire date will be one year after. here is the code:

2.                 $("#<%=txtJoinDate.ClientID %>").datepicker({
3.                     
4.                     altField:"#<%=txtExpireDate.ClientID%>"
5.                 });