I have two fields .. field1 and field2 in which value will be entered and a 3rd field....... field3 which will be equal to field 1 + field 2 .
I want the calculation to be performed when i click a action button say "button1"
this.getField("field3").value = this.getField("field1").value + this.getField("field2").value;
In what way is it not working? What happens when you click the button? Are there any error messages in the JS Console?