react component did 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 on update

const isInitialMount = useRef(true);

useEffect(() => {
  if (isInitialMount.current) {
     isInitialMount.current = false;
  } else {
      // Your useEffect code here to be run on update
  }
});