1useEffect(() => {
2 function handleStatusChange(status) {
3 setIsOnline(status.isOnline);
4 }
5 ChatAPI.subscribeToFriendStatus(props.friend.id, handleStatusChange);
6 // Specify how to clean up after this effect:
7 return () => {
8 ChatAPI.unsubscribeFromFriendStatus(props.friend.id, handleStatusChange);
9 };
10 });
1import React, { useEffect } from 'react';
2
3export const App: React.FC = () => {
4
5 useEffect(() => {
6
7 }, [/*Here can enter some value to call again the content inside useEffect*/])
8
9 return (
10 <div>Use Effect!</div>
11 );
12}
1useEffect(() => {
2 window.addEventListener('mousemove', () => {});
3
4 // returned function will be called on component unmount
5 return () => {
6 window.removeEventListener('mousemove', () => {})
7 }
8}, [])