populate textbox in succession

hi everyone

sorryfor mybadEnglish, I have a series oftextboxesthatare populatedwith buttons, but I would likethat if atextboxisalreadyoccupied, thefollowingispopulated. I'm makingan orderforthe products,andeach buttonisa product.I'll postan example.

var f = this.getField("cod")

f.value = "art51";

var f = this.getField("desc")

f.value = "coppia di contenitori 120X80";

var f = this.getField("prez")

f.value = "300";

i have a 10 textbox cod.0 - cod.10

             10 textbox desc.0 - desc.10 ecc..

I hope I didunderstand myproblemandcan help methanks to all