how to use react memo hooks

function moviePropsAreEqual(prevMovie, nextMovie) {
  return prevMovie.title === nextMovie.title
    && prevMovie.releaseDate === nextMovie.releaseDate;
}

const MemoizedMovie2 = React.memo(Movie, moviePropsAreEqual);const computeLetterCount = word => {
    let i = 0;
    while (i < 1000000000) i++;
    return word.length;
  };

  // Memoize computeLetterCount so it uses cached return value if input array ...
  // ... values are the same as last time the function was run.
  const letterCount = useMemo(() => computeLetterCount(word), [word]);