Swatch Internet Time: Vanilla JS PWA

version 0.1.0

A plain vanilla Javascript PWA app to display the current Swatch Internet Time. This is the "no frills" version which just displays the current .beat time with no additional features.

Screenshot

Online example: https://kendawson.online/free/swatch/

About

This version has a service-worker and manifest and can be installed locally as a PWA (on supported devices).

The primary Javascript function for generating the Swatch Internet Time is as follows:

function getSwatchTime() {
    const d = new Date();

    // Seconds since UTC midnight
    const utcSeconds = d.getUTCHours() * 3600 + d.getUTCMinutes() * 60 + d.getUTCSeconds();

    // Convert to Biel time (UTC+1, no DST) and wrap to 0-86399
    const bielSeconds = (utcSeconds + 3600 + 24 * 3600) % (24 * 3600);

    // 1 beat = 86.4 seconds, keep result in 0-999 and pad
    const beats = String(Math.floor(bielSeconds / 86.4) % 1000).padStart(3, '0');

    // Return string with current Swatch time (e.g. @042)
    return `@${beats}`;
}

The magic explained:

const beats = String(Math.floor(bielSeconds / 86.4) % 1000).padStart(3, '0');

Note: Rounding and display (important)

If you display centibeats (two decimals) be careful when rounding. A raw beat value like 999.995 can round to 1000.00 which is invalid for display — the correct display is 000.00. To avoid a transient 1000.00 flash, round then wrap values >=1000 back into range before formatting:

const rawBeats = bielSeconds / 86.4;
let rounded = Math.round(rawBeats * 100) / 100;
if (rounded >= 1000) rounded = rounded - 1000;
const display = rounded.toFixed(2); // safe to show

• bielSeconds is the number of seconds since midnight in Biel time (UTC+1, no DST), computed from UTC time.
• Divide by 86.4 to convert seconds to Swatch beats (86400 seconds/day => 1000 beats).
• Math.floor(...) gives the integer beat number.
• % 1000 ensures the beat wraps into the 0-999 range.
• .padStart(3, '0') pads the number with leading zeros to always produce 3 digits.

Links:

• About Swatch Internet Time: https://www.swatch.com/en-us/internet-time.html
• Github: https://github.com/swatchtime