List specific items in LB2 by the choice of LB1.

Try something like this as 'On Blur' action of "List Box1" field:

var L2 = this.getField("List Box2");
var cList2 = [];
var v = event.target.value;

if (typeof v === "object" && v !== null) {
 for (var i=0; i<v.length; i++) {
  if (v[i] === "Fruits")
   cList2.push("Banana", "Orange", "Apple");       
  if (v[i] === "Vegetables")
   cList2.push("Rice", "Carrot");}}

// If only one item is selected
else if (typeof v === "string") {    
 if (v === "Fruits")
  cList2.push("Banana", "Orange", "Apple");
 else if (v === "Vegetables")
  cList2.push("Rice", "Carrot");}

L2.clearItems();
L2.setItems(cList2);