cur_frm.cscript.custom_validate = function(doc){

    wn.call({
            method:"webnotes.client.get_value",
                args: {
                        doctype:"Customer",
                        fieldname: "customer_name",
                        filters: {
                            id_number: doc.id_number
                        },
                },
            callback: function(r) {
                    console.log(r);
                    msgprint((r.message), "already exists!");
                    validated = false;
            }

        });

}