Derive one item value from 2 other supplied values

Question

I have a form that has 3 fields. One is a renewal_date (date) field, one is a maintenance_term (number - in months) field, and the third is an expiration_date (date) field which I would like to use the add_months functionality to derive this value based on the renewal and maintenance_term. What is the easiest way to accomplish this task?

Answer 1

Hi,
You need to add some javascript to your page and call this either in the onchange or onblur events of both items. The script should be something like:
<script type="text/javascript">
function calc()
var d = document.getElementById("P50_RENEWAL_DATE").value;
var m = document.getElementById("P50_MAINT_TERM").value;
if (d != '' && m != '')
   var t = document.getElementById("P50_MAINT_EXPIRY_DATE");
   var tmp = new Date(d);
   var tmp2 = new Date(tmp.getFullYear(), tmp.getMonth() + parseInt(m), tmp.getDate());
   var dd = tmp2.getDate();
   var mm = tmp2.getMonth() + 1;
   var yy = tmp2.getFullYear();
   var out = lpad(mm) + '/' + lpad(dd) + '/' + yy;
   t.value = out;
function lpad(n)
var s = "00" + n;
var l = s.length;
return s.substring(l - 2);
</script>Update your items and add the following in the HTML Form Element Attributes for each:
onchange="javascript:calc();"or
onblur="javascript:calc();"You'll have to see which version works for your page.
Be warned that this javascript assumes that the date is entered in American date format (mm/dd/yyyy) - if it is in any other format, the function will not work.
Andy