Convert CSV data in text field to a List in anther text field

Trying to Document-Level JavaScript to get comma separated values shown in one text field to show as a list in another multiline text field. 

Example (csv): 1SZ,ATT,FHS,GU6

Needed Result: 

1SZ

ATT

FHS

GU6

Current Document Level Javascript (no success):

function StockOptions(){
var stkOpt = this.getField("List_Options").valueAsString.split(",");
var oldValue = this.getField("Factory_Options").valueAsString;

this.getField("Factory_Options").setItems(stkOpt);
if(stkOpt.indexof(oldValue)!=-1) this.getField("Factory_Options").value = oldValue;
}