Javascript OnLoad

Sergey,
I have a nice javascript onload for add page (that you showed me how to do) which breaks "totalitems" field value (let say 5) into digits 1,2,3,4,5 ("Item" field) which I can then select from dropdown. it works great, but will not work in master-child where "JobNo" is inserted automatically. Dropdown box will not pickup values. If i "ADD" in this table standalone, it works because I have to select "JobNo". How can I make this work?
Thanks,

Nash