Add optional JS countdown timer

Overview:

As a user I would like a visual indicator of how long until the next refresh synced with the designated interval, such as a countdown timer.
Auto-refresh is an excellent Streamlit component extension that solves a frequent issue - refreshing Streamlit component or page in a non-blocking manner.
Because auto-refresh utilizes an interval timer, having a synced visual indicator would be a natural functionality extension.

Details:

Add optional html/js timer functionality.
Allow initialization option to turn countdown timer on - defaults to False.
Allow initialization option to specify desired countdown timer text.

Proposed Solution:

<script>
    function startTimer(duration, display) {{
        var timer = duration, minutes, seconds;
        setInterval(function () {{
            minutes = parseInt(timer / 60, 10)
            seconds = parseInt(timer % 60, 10);

            minutes = minutes < 10 ? "0" + minutes : minutes;
            seconds = seconds < 10 ? "0" + seconds : seconds;

            display.textContent = minutes + ":" + seconds;

            if (--timer < 0) {{
                timer = duration;
            }}
        }}, 1000);
    }}

    window.onload = function () {{
        var duration = 60 * 5 ,
        display = document.querySelector('#time'),
        startTimer(duration, display);
    }};
</script>

<body style="font-family: 'Source Sans Pro', sans-serif; line-height: 24px; font-size: 1rem;">
    <div style="color: white">Next refresh in approx: <span id="time">5:00</span></div>
</body>

Notes:

I ran the gamut trying time.sleep, asyncio.sleep, and html/js based timers, but they all either blocked or were out of sync with the interval. I don't actually care that the interval is exactly the specified amount of time (5 minutes, for example), but I'd like for the countdown timer to be generally in-sync with the interval, and more importantly, clear and reset when the interval resets.
HTML example shamelessly borrowed from this streamlit forum post.
Also open to some other mechanism of syncing countdown timers, this is just the one that came to mind.
As a side note, this component functionality is essential enough it should be pulled into Streamlit core.

kmcgrady / streamlit-autorefresh

Add optional JS countdown timer #11

Overview:

Details:

Proposed Solution:

Notes: