next.js/examples/with-redux-saga/components/clock.js

import React from 'react'

const pad = n => (n < 10 ? `0${n}` : n)

const format = t => {
  const hours = t.getUTCHours()
  const minutes = t.getUTCMinutes()
  const seconds = t.getUTCSeconds()
  return `${pad(hours)}:${pad(minutes)}:${pad(seconds)}`
}

function Clock ({ lastUpdate, light }) {
  return (
    <div className={light ? 'light' : ''}>
      {format(new Date(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