web/node_modules/moment/src/lib/duration/iso-string.js

import absFloor from '../utils/abs-floor';
var abs = Math.abs;

function sign(x) {
    return ((x > 0) - (x < 0)) || +x;
}

export function toISOString() {
    // for ISO strings we do not use the normal bubbling rules:
    //  * milliseconds bubble up until they become hours
    //  * days do not bubble at all
    //  * months bubble up until they become years
    // This is because there is no context-free conversion between hours and days
    // (think of clock changes)
    // and also not between days and months (28-31 days per month)
    if (!this.isValid()) {
        return this.localeData().invalidDate();
    }

    var seconds = abs(this._milliseconds) / 1000;
    var days         = abs(this._days);
    var months       = abs(this._months);
    var minutes, hours, years;

    // 3600 seconds -> 60 minutes -> 1 hour
    minutes           = absFloor(seconds / 60);
    hours             = absFloor(minutes / 60);
    seconds %= 60;
    minutes %= 60;

    // 12 months -> 1 year
    years  = absFloor(months / 12);
    months %= 12;


    // inspired by https://github.com/dordille/moment-isoduration/blob/master/moment.isoduration.js
    var Y = years;
    var M = months;
    var D = days;
    var h = hours;
    var m = minutes;
    var s = seconds ? seconds.toFixed(3).replace(/\.?0+$/, '') : '';
    var total = this.asSeconds();

    if (!total) {
        // this is the same as C#'s (Noda) and python (isodate)...
        // but not other JS (goog.date)
        return 'P0D';
    }

    var totalSign = total < 0 ? '-' : '';
    var ymSign = sign(this._months) !== sign(total) ? '-' : '';
    var daysSign = sign(this._days) !== sign(total) ? '-' : '';
    var hmsSign = sign(this._milliseconds) !== sign(total) ? '-' : '';

    return totalSign + 'P' +
        (Y ? ymSign + Y + 'Y' : '') +
        (M ? ymSign + M + 'M' : '') +
        (D ? daysSign + D + 'D' : '') +
        ((h || m || s) ? 'T' : '') +
        (h ? hmsSign + h + 'H' : '') +
        (m ? hmsSign + m + 'M' : '') +
        (s ? hmsSign + s + 'S' : '');
}