react state useeffect code example
Example 1: useEffect
import React, { useState, useEffect } from 'react';
function Example() {
const [count, setCount] = useState(0);
// Similar to componentDidMount and componentDidUpdate:
useEffect(() => {
// Update the document title using the browser API
document.title = `You clicked ${count} times`;
});
return (
You clicked {count} times
);
}
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);
};
});