PHP's date in JavaScript

module.exports = functiondate (format, timestamp) {
//  discuss at: https://locutus.io/php/date/
// original by: Carlos R. L. Rodrigues (https://www.jsfromhell.com)
// original by: gettimeofday
//    parts by: Peter-Paul Koch (https://www.quirksmode.org/js/beat.html)
// improved by: Kevin van Zonneveld (https://kvz.io)
// improved by: MeEtc (https://yass.meetcweb.com)
// improved by: Brad Touesnard
// improved by: Tim Wiel
// improved by: Bryan Elliott
// improved by: David Randall
// improved by: Theriault (https://github.com/Theriault)
// improved by: Theriault (https://github.com/Theriault)
// improved by: Brett Zamir (https://brett-zamir.me)
// improved by: Theriault (https://github.com/Theriault)
// improved by: Thomas Beaucourt (https://www.webapp.fr)
// improved by: JT
// improved by: Theriault (https://github.com/Theriault)
// improved by: Rafał Kukawski (https://blog.kukawski.pl)
// improved by: Theriault (https://github.com/Theriault)
//    input by: Brett Zamir (https://brett-zamir.me)
//    input by: majak
//    input by: Alex
//    input by: Martin
//    input by: Alex Wilson
//    input by: Haravikk
// bugfixed by: Kevin van Zonneveld (https://kvz.io)
// bugfixed by: majak
// bugfixed by: Kevin van Zonneveld (https://kvz.io)
// bugfixed by: Brett Zamir (https://brett-zamir.me)
// bugfixed by: omid (https://locutus.io/php/380:380#comment_137122)
// bugfixed by: Chris (https://www.devotis.nl/)
//      note 1: Uses global: locutus to store the default timezone
//      note 1: Although the function potentially allows timezone info
//      note 1: (see notes), it currently does not set
//      note 1: per a timezone specified by date_default_timezone_set(). Implementers might use
//      note 1: $locutus.currentTimezoneOffset and
//      note 1: $locutus.currentTimezoneDST set by that function
//      note 1: in order to adjust the dates in this function
//      note 1: (or our other date functions!) accordingly
//   example 1: date('H:m:s \\m \\i\\s \\m\\o\\n\\t\\h', 1062402400)
//   returns 1: '07:09:40 m is month'
//   example 2: date('F j, Y, g:i a', 1062462400)
//   returns 2: 'September 2, 2003, 12:26 am'
//   example 3: date('Y W o', 1062462400)
//   returns 3: '2003 36 2003'
//   example 4: var $x = date('Y m d', (new Date()).getTime() / 1000)
//   example 4: $x = $x + ''
//   example 4: var $result = $x.length // 2009 01 09
//   returns 4: 10
//   example 5: date('W', 1104534000)
//   returns 5: '52'
//   example 6: date('B t', 1104534000)
//   returns 6: '999 31'
//   example 7: date('W U', 1293750000.82); // 2010-12-31
//   returns 7: '52 1293750000'
//   example 8: date('W', 1293836400); // 2011-01-01
//   returns 8: '52'
//   example 9: date('W Y-m-d', 1293974054); // 2011-01-02
//   returns 9: '52 2011-01-02'
//        test: skip-1 skip-2 skip-5
let jsdate, f
// Keep this here (works, but for code commented-out below for file size reasons)
// var tal= [];
const txtWords = [
'Sun', 'Mon', 'Tues', 'Wednes', 'Thurs', 'Fri', 'Satur',
'January', 'February', 'March', 'April', 'May', 'June',
'July', 'August', 'September', 'October', 'November', 'December'
  ]
// trailing backslash -> (dropped)
// a backslash followed by any character (including backslash) -> the character
// empty string -> empty string
const formatChr = /\\?(.?)/gi
const formatChrCb = function (t, s) {
return f[t] ? f[t]() : s
  }
const _pad = function (n, c) {
    n = String(n)
while (n.length < c) {
      n = '0' + n
    }
return n
  }
  f = {
// Day
    d: function () {
// Day of month w/leading 0; 01..31
return _pad(f.j(), 2)
    },
D: function () {
// Shorthand day name; Mon...Sun
return f.l()
        .slice(0, 3)
    },
j: function () {
// Day of month; 1..31
return jsdate.getDate()
    },
l: function () {
// Full day name; Monday...Sunday
return txtWords[f.w()] + 'day'
    },
N: function () {
// ISO-8601 day of week; 1[Mon]..7[Sun]
return f.w() || 7
    },
S: function () {
// Ordinal suffix for day of month; st, nd, rd, th
const j = f.j()
let i = j % 10
if (i <= 3 && parseInt((j % 100) / 10, 10) === 1) {
        i = 0
      }
return ['st', 'nd', 'rd'][i - 1] || 'th'
    },
w: function () {
// Day of week; 0[Sun]..6[Sat]
return jsdate.getDay()
    },
z: function () {
// Day of year; 0..365
const a = newDate(f.Y(), f.n() - 1, f.j())
const b = newDate(f.Y(), 0, 1)
returnMath.round((a - b) / 864e5)
    },
// Week
    W: function () {
// ISO-8601 week number
const a = newDate(f.Y(), f.n() - 1, f.j() - f.N() + 3)
const b = newDate(a.getFullYear(), 0, 4)
return _pad(1 + Math.round((a - b) / 864e5 / 7), 2)
    },
// Month
    F: function () {
// Full month name; January...December
return txtWords[6 + f.n()]
    },
m: function () {
// Month w/leading 0; 01...12
return _pad(f.n(), 2)
    },
M: function () {
// Shorthand month name; Jan...Dec
return f.F()
        .slice(0, 3)
    },
n: function () {
// Month; 1...12
return jsdate.getMonth() + 1
    },
t: function () {
// Days in month; 28...31
return (newDate(f.Y(), f.n(), 0))
        .getDate()
    },
// Year
    L: function () {
// Is leap year?; 0 or 1
const j = f.Y()
return j % 4 === 0 & j % 100 !== 0 | j % 400 === 0
    },
o: function () {
// ISO-8601 year
const n = f.n()
const W = f.W()
const Y = f.Y()
return Y + (n === 12 && W < 9 ? 1 : n === 1 && W > 9 ? -1 : 0)
    },
Y: function () {
// Full year; e.g. 1980...2010
return jsdate.getFullYear()
    },
y: function () {
// Last two digits of year; 00...99
return f.Y()
        .toString()
        .slice(-2)
    },
// Time
    a: function () {
// am or pm
return jsdate.getHours() > 11 ? 'pm' : 'am'
    },
A: function () {
// AM or PM
return f.a()
        .toUpperCase()
    },
B: function () {
// Swatch Internet time; 000..999
const H = jsdate.getUTCHours() * 36e2
// Hours
const i = jsdate.getUTCMinutes() * 60
// Minutes
// Seconds
const s = jsdate.getUTCSeconds()
return _pad(Math.floor((H + i + s + 36e2) / 86.4) % 1e3, 3)
    },
g: function () {
// 12-Hours; 1..12
return f.G() % 12 || 12
    },
G: function () {
// 24-Hours; 0..23
return jsdate.getHours()
    },
h: function () {
// 12-Hours w/leading 0; 01..12
return _pad(f.g(), 2)
    },
H: function () {
// 24-Hours w/leading 0; 00..23
return _pad(f.G(), 2)
    },
i: function () {
// Minutes w/leading 0; 00..59
return _pad(jsdate.getMinutes(), 2)
    },
s: function () {
// Seconds w/leading 0; 00..59
return _pad(jsdate.getSeconds(), 2)
    },
u: function () {
// Microseconds; 000000-999000
return _pad(jsdate.getMilliseconds() * 1000, 6)
    },
// Timezone
    e: function () {
// Timezone identifier; e.g. Atlantic/Azores, ...
// The following works, but requires inclusion of the very large
// timezone_abbreviations_list() function.
/*              return that.date_default_timezone_get();
       */
const msg = 'Not supported (see source code of date() for timezone on how to add support)'
thrownewError(msg)
    },
I: function () {
// DST observed?; 0 or 1
// Compares Jan 1 minus Jan 1 UTC to Jul 1 minus Jul 1 UTC.
// If they are not equal, then DST is observed.
const a = newDate(f.Y(), 0)
// Jan 1
const c = Date.UTC(f.Y(), 0)
// Jan 1 UTC
const b = newDate(f.Y(), 6)
// Jul 1
// Jul 1 UTC
const d = Date.UTC(f.Y(), 6)
return ((a - c) !== (b - d)) ? 1 : 0
    },
O: function () {
// Difference to GMT in hour format; e.g. +0200
const tzo = jsdate.getTimezoneOffset()
const a = Math.abs(tzo)
return (tzo > 0 ? '-' : '+') + _pad(Math.floor(a / 60) * 100 + a % 60, 4)
    },
P: function () {
// Difference to GMT w/colon; e.g. +02:00
const O = f.O()
return (O.substr(0, 3) + ':' + O.substr(3, 2))
    },
T: function () {
// The following works, but requires inclusion of the very
// large timezone_abbreviations_list() function.
/*              var abbr, i, os, _default;
      if (!tal.length) {
        tal = that.timezone_abbreviations_list();
      }
      if ($locutus && $locutus.default_timezone) {
        _default = $locutus.default_timezone;
        for (abbr in tal) {
          for (i = 0; i < tal[abbr].length; i++) {
            if (tal[abbr][i].timezone_id === _default) {
              return abbr.toUpperCase();
            }
          }
        }
      }
      for (abbr in tal) {
        for (i = 0; i < tal[abbr].length; i++) {
          os = -jsdate.getTimezoneOffset() * 60;
          if (tal[abbr][i].offset === os) {
            return abbr.toUpperCase();
          }
        }
      }
      */
return'UTC'
    },
Z: function () {
// Timezone offset in seconds (-43200...50400)
return -jsdate.getTimezoneOffset() * 60
    },
// Full Date/Time
    c: function () {
// ISO-8601 date.
return'Y-m-d\\TH:i:sP'.replace(formatChr, formatChrCb)
    },
r: function () {
// RFC 2822
return'D, d M Y H:i:s O'.replace(formatChr, formatChrCb)
    },
U: function () {
// Seconds since UNIX epoch
return jsdate / 1000 | 0
    }
  }
const _date = function (format, timestamp) {
    jsdate = (timestamp === undefined
      ? newDate() // Not provided
      : (timestamp instanceofDate)
          ? newDate(timestamp) // JS Date()
          : newDate(timestamp * 1000) // UNIX timestamp (auto-convert to int)
    )
return format.replace(formatChr, formatChrCb)
  }
return _date(format, timestamp)
}