CODE EXAMPLE FOR JAVASCRIPT

useEffect : react

import { useState, useEffect } from 'react';

function App() {

  const [pieceOfState, setPieceOfState] = useState(0);

  useEffect(() => {
    console.log('I'm in useEffect!');
    console.log('This will be called whenever an instance of this component mounts');
    console.log('or whenever pieceOfState is updated');
  }, [pieceOfState]);

  return (
    <div>
      <button onClick={() => setPieceOfState(pieceOfState + 1)}>Click Me to Update pieceOfState!</button>
    </div>
  );
}