class Order{} 

class OnlineOrder extends Order{} 

class OfflineOrder extends Order{} 

function save(service:{ getOrder(): Order }, dbConnection: any) { 

    const order = service.getOrder(); 

    if (order instanceof OnlineOrder) 

        addOnlineOrder(order, dbConnection); 

    else 

        addOfflineOrder((order as OfflineOrder), dbConnection); 

} 

function addOnlineOrder(order:OnlineOrder, dbConnection: any){ 

  // Online order processing 

} 

function addOfflineOrder(order:OfflineOrder, dbConnection: any){ 

  // Offline order processing 

}