use effect input called code example
Example 1: useeffect with cleanup
useEffect(() => {
//your code goes here
return () => {
//your cleanup code codes here
};
},[]);
Example 2: useeffect componentdidmount
useEffect(() => {
messagesRef.on('child added', snapshot => {
const message = snapshot.val();
message.key = snapshot.key;
setMessages(messages.concat(message)); // See Note 1
}, []); // See Note 2