react hooks mount functional component code example
Example 1: how to use componentdidmount in functional component
// passing an empty array as second argument triggers the callback in useEffect
// only after the initial render thus replicating `componentDidMount` lifecycle behaviour
useEffect(() => {
if(!props.fetched) {
props.fetchRules();
}
console.log('mount it!');
}, []);
// componentDidUpdate
useEffect({
your code here
})
// For componentDidUpdate
useEffect(() => {
// Your code here
}, [yourDependency]);
// For componentWillUnmount
useEffect(() => {
// componentWillUnmount
return () => {
// Your code here
}
}, [yourDependency]);
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