Not working computation.?

ill try to create another field to sum the net total and Taxes and Charges Added the problem is cant display i want to display in my Debit to Field. need help

this is my code:

frappe.ui.form.on(“Purchase Invoice”, “net_total”, function(frm, cdt, cdn) {
var d = locals[cdt][cdn];
frappe.model.set_value(cdt, cdn, “total_debit”, d.taxes_and_charges_added + d.net_total);