Generate Monthly Schedule in child table

I have a start date and end date in parent doc type and i want to generate a schedule on monthly basis how can i achieve this
i tried following script but its not working
frappe.ui.form.on(‘Lease Schedule’, {
lease_invoice_schedule_add: function(frm) {
var row = cur_frm.doc.items.length - 1;
if (row === 0) {
var startdate = frm.doc.start_date
var enddate = frm.doc.end_date;
var today = startdate;
frappe.model.set_value(cur_frm.doc.items[row].doctype, cur_frm.doc.items[row].name, “date_of_installment”, today);
}
else {
var tomorrow = new Date();
tomorrow.setDate(tomorrow.getDate() + row);
frappe.model.set_value(cur_frm.doc.items[row].doctype, cur_frm.doc.items[row].name, “date_of_installment”, tomorrow);
}
cur_frm.doc.lease_invoice_schedule[i].amount = cur_frm.doc.lease_amount
cur_frm.doc.lease_invoice_schedule[i].customer = cur_frm.doc.property_owner
},
end_date: function(frm) {
frappe.model.add_child(cur_frm.doc, “Lease Schedule”, “lease_invoice_schedule”);
}
});