MyComponent.jsx

import React, { useEffect, useState, memo } from 'react';

const MyComponent = () => {
  const [foo, setFoo] = useState('foo');

  useMemo(() => {
    // componentWillMount
  }, []);

  useEffect(() => {
    // componentDidMount. If we need the DOM => "useLayoutEffect"
    fetch('/foo', {
      method: 'GET',
    })
    .then(res => res.json())
    .then(json => setFoo(json));

    return () => {
      // componentWillUnmount
    }
  }, []);

  useEffect(() => {
    // componentDidUpdate
  }, [foo]);

  return null;
}

export default memo(MyComponent); // PureComponent