UI: Time and Date

[Sineos]

I'm generating a time / date string and have it displayed via a text-node

const d = new Date;
const langCode = 'de-DE'
const options = {
    timeZone: 'Europe/Berlin',
    timeStyle: 'medium',
    dateStyle: 'medium',
    hour12: false,
};

msg.payload = d.toLocaleString(langCode, options)

return msg;

It seems the formatting options are ignored in NR-MCU:

• NR-PC: 27.02.2023, 08:15:57
• NR-MCU: Mon Feb 27 2023 08:15:57

[phoddie]

That's expected and valid because the options parameter to Date.prototype.toLocaleString is optional. The parameter is specified by ECMA-402 (e.g. Intl). XS implements the JavaScript language standard (ECMA-262), but not ECMA-402.

[phoddie]

It would be complete mayhem to store data with local time stamps

Indeed. But, JavaScript Dates are natively UTC. So, no problem.

No client browser's local time

I don't understand this point. Local time is available too.

Anyway.... If your goal is to do exactly the same things you do on the PC in exactly the same way on an MCU, you will be disappointed as you sound. MCUs can do quite a bit, but they will be a PC.

[Sineos]

Don't get me wrong, please. My experience with with MCUs is severely limited, so I just try to figure out, where and how I have to adapt. On a full fledged PC there is often "someone who is taking care about something, somehow", so I do not need to bother. On a MCU I need to learn about the differences. Many thanks for bearing with me so far. This is highly appreciated :+1

I don't understand this point. Local time is available too.

If I understood our conversation correctly so far: Yes, true until DST kicks in spoils the fun. Would not be relevant to a MCU attached to the PC but relevant for a standalone MCU application. Meaning I need to do something in a function node to catch the DST switch times and adapt my local time. Correct?

[phoddie]

It looks like with some work, it is possible to configure the ESP-IDF to manage the DST offset. That's an adventure to explore.

[tve]

On a linux system tail -1 /etc/localtime will get you the desired DST config string, assuming your system has the time zone you're looking for...

[Sineos]

For the time being I solved it like this

function node

// The end of DST in Europe is the last Sunday in March of the given year at 01:00 UTC
function getLastSundayInMarch() {
    const today = new Date();
    const year = today.getUTCFullYear();
    const lastDayOfMarch = new Date(Date.UTC(year, 2, 31, 1)); // March 31st at 01:00 UTC
    const dayOfWeek = lastDayOfMarch.getUTCDay();

    // If the last day of March is a Sunday, set the time to 01:00 UTC and return it.
    if (dayOfWeek === 0) {
        lastDayOfMarch.setUTCHours(1);
        return lastDayOfMarch;
    }

    // Otherwise, calculate the number of days to subtract from the last day of March to get to the last Sunday.
    const daysToSubtract = dayOfWeek;
    const lastSundayInMarch = new Date(Date.UTC(year, 2, 31 - daysToSubtract, 1)); // Last Sunday in March at 01:00 UTC
    return lastSundayInMarch;
}

// The begin of DST in Europe is the last Sunday in October of the given year at 01:00 UTC
function getLastSundayInOctober() {
    const today = new Date();
    const year = today.getUTCFullYear();
    const lastDayOfOctober = new Date(Date.UTC(year, 9, 31, 1)); // October 31st at 01:00 UTC
    const dayOfWeek = lastDayOfOctober.getUTCDay();

    // If the last day of October is a Sunday, set the time to 01:00 UTC and return it.
    if (dayOfWeek === 0) {
        lastDayOfOctober.setUTCHours(1);
        return lastDayOfOctober;
    }

    // Otherwise, calculate the number of days to subtract from the last day of October to get to the last Sunday.
    const daysToSubtract = dayOfWeek;
    const lastSundayInOctober = new Date(Date.UTC(year, 9, 31 - daysToSubtract, 1)); // Last Sunday in October at 01:00 UTC
    return lastSundayInOctober;
}

// Return a date / time string
function formatDate(date) {
    const day = String(date.getUTCDate()).padStart(2, '0');
    const month = String(date.getUTCMonth() + 1).padStart(2, '0');
    const year = String(date.getUTCFullYear()).slice(2);
    const hour = String(date.getUTCHours()).padStart(2, '0');
    const minute = String(date.getUTCMinutes()).padStart(2, '0');
    const second = String(date.getUTCSeconds()).padStart(2, '0');

    return `${day}.${month}.${year}, ${hour}:${minute}:${second}`;
}

// Correct the UTC time according to summer / winter DST offsets
function getDSTdate(date, dstOffsetSummer, dstOffsetWinter) {
    const lastSundayInMarch = getLastSundayInMarch();
    const lastSundayInOctober = getLastSundayInOctober();
    const dateTimestamp = date.getTime();

    if (dateTimestamp >= lastSundayInOctober.getTime() || dateTimestamp < lastSundayInMarch.getTime()) {
        date.setHours(date.getHours() + dstOffsetWinter);
    } else if (dateTimestamp >= lastSundayInMarch.getTime()) {
        date.setHours(date.getUTCHours() + dstOffsetSummer);
    }

    return formatDate(date);
}

msg.payload = getDSTdate(new Date(), 2, 1);

return msg;

While it seems to work, it is probably a very complicated way of doing it. So please do not laugh (at least not too loud) 😝