Javascript error??

I’m new to Javascript but not to programming.

When i use this snippet it works ok and field displays 180:
(function(){
var volw1 = 180;
var volwx = 60;
var kind = 50;
var ret = volw1;
return ret;
})();

But when added one line to display a date field the field doesn’t get calculated and is empty:
(function(){
var volw1 = 180;
var volwx = 60;
var kind = 50;
var ret = volw1;
windows.alert(fieldname30);
return ret;
})();

Why?

https://wordpress.org/plugins/calculated-fields-form/