useClock hook

useClock.ts

import * as React from 'react'
import useInterval from './useInterval'

export default function useClock() {
  const [time, setTime] = React.useState<Date>(new Date())

  const tick = () => {
    setTime(new Date())
  }

  useInterval(tick, 500)
  return time
}

useInterval.ts

import * as React from 'react'

/**
 * `useInterval()` hook stolen from Dan's blog:
 * https://overreacted.io/making-setinterval-declarative-with-react-hooks/
 */
export default function useInterval(callback: () => void, delay: number = 1000) {
  const savedCallback = React.useRef<any>()

  // Remember the latest callback.
  React.useEffect(() => {
    savedCallback.current = callback
  }, [callback])

  // Set up the interval.
  React.useEffect(() => {
    function tick() {
      savedCallback.current()
    }

    const id = setInterval(tick, delay)
    return () => clearInterval(id)
  }, [delay])
}