Cancel permission based on grand total

cur_frm.cscript.custom_before_cancel = function(doc) {
 if (user_roles.indexOf("Accounts User")!=-1 && user_roles.indexOf("Accounts Manager")==-1
   && user_roles.indexOf("System Manager")==-1) {
  if (flt(doc.grand_total) > 10000) {
   msgprint("You can not cancel this transaction, because grand total \
    is greater than 10000");
   validated = false;
  }
 }
}