if will i select Item no. from dropdown menu then automatically show description and price column

I have successfully easily entered item no. on the drop-down menu but I am still facing the issue of not showing the description and prices. Please check 2 attachment of screenshot

I am adding a simple fillable box in the description and unit cost. do I need also a dropdown menu in the description and unit cost?

I am going to item no. property and go to  'Custom calculation script'  and add the below script

var cData = [
{item: "Item1", desc: "Description1", cost: 100},
{item: "Item2", desc: "Description2", cost: 120},
{item: "Item3", desc: "Description3", cost: 150}];

if(event.value !== "Select item"){
for(var i=0; i<cData.length; i++){
if(event.value == cData[i].item){
this.getField("description").value = cData[i].desc;
this.getField("Unit Cost").value = cData[i].cost;
break;}}}
else {
this.getField("description").value = "";
this.getField("Unit Cost").value = "";}