Get field value from Item to Purchase order master field

I created 2 fields on item table (def_sqm and def_box) and i store value according each item name

I also created same fields in purchase order item (both doc type is LINK with item), i wnat when i select iten code in purchase order table , same time def_sqm and def_boxes value populate in the fileld.

I try to create customise script on the purchase order

frappe.ui.form.on(“item”, {
“def_sqm”: function(frm) {
frm.add_fetch(“def_sqm”, “def_sqm”, “def_sqm”);

Please help me , thanks