tz.js/index.js

"use strict";

function fromUTCToTimeZone(date, timeZone) {
    // ISO string or existing date object
    date = new Date(date);
    var options = {
        timeZone: timeZone,
        year: "numeric",
        month: "numeric",
        day: "numeric",
        hour12: false,
        hour: "numeric",
        minute: "numeric",
        second: "numeric",
        fractionalSecondDigits: 3,
    };

    var tzOptions = Object.assign(
        {
            timeZoneName: "long",
        },
        options
    );

    // Every country uses the same year and months, right?
    var formater = new Intl.DateTimeFormat("default", tzOptions);
    var parts = formater.formatToParts(date);

    var whole = {};
    parts.forEach(function (part) {
        var val = part.value;
        switch (part.type) {
            case "literal":
                // ignore separators and whitespace characters
                return;
            case "timeZoneName":
                // keep as is - it's a string
                break;
            case "month":
                // months are 0-indexed for new Date()
                val = parseInt(val, 10) - 1;
                break;
            case "hour":
                // because sometimes 24 is used instead of 0, make 24 0
                val = parseInt(val, 10) % 24;
                break;
            case "fractionalSecond":
                // fractionalSecond is a dumb name - should be millisecond
                whole.millisecond = parseInt(val, 10);
                return;
            default:
                val = parseInt(val, 10);
        }
        // whole.month = 0;
        whole[part.type] = val;
    });

    whole.timeZone = timeZone;
    whole.offset = getOffset(date, whole);
    whole.toISOString = _toOffsetISOString;
    return whole;
}

function _toOffsetISOString() {
    return toOffsetISOString(this);
}

function getOffset(utcDate, tzD2) {
    var tzDate = new Date(toOffsetISOString(tzD2));
    var diff = Math.round(tzDate.valueOf() - utcDate.valueOf()) / (60 * 1000);
    return diff;
}

function p2(x) {
    return String(x).padStart(2, "0");
}

function p3(x) {
    return String(x).padStart(3, "0");
}

function formatOffset(minutes) {
    if (!minutes) {
        return "Z";
    }

    var h = Math.floor(Math.abs(minutes) / 60);
    var m = Math.abs(minutes) % 60;
    var offset = "";
    if (minutes > 0) {
        offset = "+";
    } else if (minutes < 0) {
        offset = "-";
    }

    // +0500, -0730
    return (
        offset + h.toString().padStart(2, "0") + m.toString().padStart(2, "0")
    );
}

function toOffsetISOString(d) {
    var offset = formatOffset(d.offset);
    return (
        `${d.year}-${p2(d.month + 1)}-${p2(d.day)}` +
        `T${p2(d.hour)}:${p2(d.minute)}:${p2(d.second)}.${p3(
            d.millisecond
        )}${offset}`
    );
}

function fromZonedToUTC(dt, tz) {}

module.exports = {
    // bespoke date =>
    // 2021-11-07T3:15:59-0500
    toOffsetISOString: toOffsetISOString,
    // -240 => -0400
    formatOffset: formatOffset,
    // [ "2021-11-07T08:15:59Z", "America/New_York" ]
    // => "2021-11-07T03:15:59-0500" // 2021-11-07 03:15:59
    fromUTCToTimeZone: fromUTCToTimeZone,
    // [ "2021-11-07 03:15:59", "America/New_York" ]
    // => "2021-11-07T03:15:59-0500" // 2021-11-07T08:15:59Z
    fromZonedToUTC: fromZonedToUTC,
};