Run an effect code example

Example 1: useeffect react

useEffect(() => {
	//  code goes here
    return () => {
      // cleanup code codes here
    };
  },[]);

Example 2: clean up useeffect

useEffect(() => {
    function handleStatusChange(status) {
      setIsOnline(status.isOnline);
    }
    ChatAPI.subscribeToFriendStatus(props.friend.id, handleStatusChange);
    // Specify how to clean up after this effect:
    return () => {
      ChatAPI.unsubscribeFromFriendStatus(props.friend.id, handleStatusChange);
    };
  });