Here is something from my Invoice Detail page on my Web database at
www.bullschmidt.com/login.asp.
It calls a few of my library functions but hopefully even without thoses specific details this might give you some JavaScript ideas about it.
<script type="text/javascript"> <!--
function jsRecalcPg() {
// Dim var.
var frm;
var strInvDetailProdDescr;
var varInvDetailProdPrice;
var varInvDetailQty;
var varInvDetailTotal;
// Form.
frm = document.frmMain;
// InvDetailProdDescr.
// Retrieve from combo.
strInvDetailProdDescr = frm.InvDetailProdID.options[frm.InvDetailProdID.selectedIndex].text;
// Truncate to just the desired col.
strInvDetailProdDescr = strInvDetailProdDescr.substring(21, 41);
// Trim.
strInvDetailProdDescr = jpsjsTrim(strInvDetailProdDescr);
// Set form fld.
frm.InvDetailProdDescr.value = strInvDetailProdDescr;
// InvDetailProdPrice.
// Retrieve from combo.
varInvDetailProdPrice = frm.InvDetailProdID.options[frm.InvDetailProdID.selectedIndex].text;
// Truncate to just the desired col.
varInvDetailProdPrice = varInvDetailProdPrice.substring(42, 52);
// Trim.
varInvDetailProdPrice = jpsjsTrim(varInvDetailProdPrice);
// Set form fld.
frm.InvDetailProdPrice.value = varInvDetailProdPrice;
// InvDetailTotal.
// Convert to nums.
varInvDetailProdPrice = jpsjsCNum(varInvDetailProdPrice);
varInvDetailQty = jpsjsCNum(frm.InvDetailQty.value);
// Multiply & round.
varInvDetailTotal = jpsjsRound(varInvDetailProdPrice * varInvDetailQty, 2);
// Format.
varInvDetailTotal = jpsjsFormat(varInvDetailTotal, "type:number;pattern:$,0.00;neg

)");
// Set form fld.
frm.InvDetailTotal.value = varInvDetailTotal;
}
//-->
</script>