Set default print format no longer working in v15

ERPNext Customize ERPNext
1

The following JavaScript works for all versions < v15. May someone assist and get it working for v15:frappe.ui.form.on

('Purchase Order', {
    refresh(frm) {
        if (cur_frm.doc.grand_total> 5000) 
		{
			
			frm.meta.default_print_format = "ApprovalTemplate";
     
        }
    }
});