socket.io 使用效果清理 function 反应

Question

I am calling socket.on function inside component but I want to stop it when the component unmount, I'm using a functional component.

useEffect(() => {
    socket.on("new-chat-message", (firstname, lastname, content, date) => {
      dispatch(
        addMessage({
          firstname: firstname,
          lastname: lastname,
          content: content,
          date: date,
        })
      );
    });
  }, [dispatch, socket]);

I need to know how to set the cleanup function for this useEffect.

Answer 1

As explained in the doc here

useEffect(() => {
    const callback = (firstname, lastname, content, date) => {
      dispatch(
        addMessage({
          firstname: firstname,
          lastname: lastname,
          content: content,
          date: date,
        })
      );
    }

    socket.on("new-chat-message", callback);

    return () => {
       socket.off("new-chat-message", callback);
    }
}, [dispatch, socket]);