vercel__next.js/examples/with-apollo-and-redux/components/Clock.js

import { useSelector, shallowEqual } from "react-redux";

const useClock = () => {
  return useSelector(
    (state) => ({
      lastUpdate: state.lastUpdate,
      light: state.light,
    }),
    shallowEqual,
  );
};

const formatTime = (time) => {
  // cut off except hh:mm:ss
  return new Date(time).toJSON().slice(11, 19);
};

const Clock = () => {
  const { lastUpdate, light } = useClock();
  return (
    <div className={light ? "light" : ""}>
      {formatTime(lastUpdate)}
      <style jsx>{`
        div {
          padding: 15px;
          display: inline-block;
          color: #82fa58;
          font:
            50px menlo,
            monaco,
            monospace;
          background-color: #000;
        }
        .light {
          background-color: #999;
        }
      `}</style>
    </div>
  );
};

export default Clock;