vs code screenshot

Typescript does NOT show errors or warnings when accessing undefined property:

export type Chat = {
  id: string;
  members: ChatUser[];
  name?: string;
  messages?: Message[] | undefined;
  order?: string;
  _count: { messages: number };
};

const newChat: Chat = {
  id: "1",
  members: [{ id: "1", login: "test", isOnline: true }],
  _count: { messages: 0 },
};

const lastMessage = newChat.messages[0];

const isRead = lastMessage.isRead;

BUT I get lastMessage is undefined in runtime.

what can i do to catch undefined value before runtime?

I tried explicitly setting the type of lastMessage to Message | undefined but I still get const lastMessage: Message from Typescript