PHP's idate in JavaScript

module.exports = functionidate (format, timestamp) {
//  discuss at: https://locutus.io/php/idate/
// original by: Brett Zamir (https://brett-zamir.me)
// original by: date
// original by: gettimeofday
//    input by: Alex
// bugfixed by: Brett Zamir (https://brett-zamir.me)
// improved by: Theriault (https://github.com/Theriault)
//   example 1: idate('y', 1255633200)
//   returns 1: 9
if (format === undefined) {
thrownewError('idate() expects at least 1 parameter, 0 given')
  }
if (!format.length || format.length > 1) {
thrownewError('idate format is one char')
  }
// @todo: Need to allow date_default_timezone_set() (check for $locutus.default_timezone and use)
const _date = (typeof timestamp === 'undefined')
    ? newDate()
    : (timestamp instanceofDate)
        ? newDate(timestamp)
        : newDate(timestamp * 1000)
let a
switch (format) {
case'B':
returnMath.floor((
        (_date.getUTCHours() * 36e2) +
        (_date.getUTCMinutes() * 60) +
        _date.getUTCSeconds() + 36e2
      ) / 86.4) % 1e3
case'd':
return _date.getDate()
case'h':
return _date.getHours() % 12 || 12
case'H':
return _date.getHours()
case'i':
return _date.getMinutes()
case'I':
// capital 'i'
// Logic original by getimeofday().
// Compares Jan 1 minus Jan 1 UTC to Jul 1 minus Jul 1 UTC.
// If they are not equal, then DST is observed.
      a = _date.getFullYear()
return0 + (((newDate(a, 0)) - Date.UTC(a, 0)) !== ((newDate(a, 6)) - Date.UTC(a, 6)))
case'L':
      a = _date.getFullYear()
return (!(a & 3) && (a % 1e2 || !(a % 4e2))) ? 1 : 0
case'm':
return _date.getMonth() + 1
case's':
return _date.getSeconds()
case't':
return (newDate(_date.getFullYear(), _date.getMonth() + 1, 0))
        .getDate()
case'U':
returnMath.round(_date.getTime() / 1000)
case'w':
return _date.getDay()
case'W':
      a = newDate(
        _date.getFullYear(),
        _date.getMonth(),
        _date.getDate() - (_date.getDay() || 7) + 3
      )
return1 + Math.round((a - (newDate(a.getFullYear(), 0, 4))) / 864e5 / 7)
case'y':
returnparseInt((_date.getFullYear() + '')
        .slice(2), 10) // This function returns an integer, unlike _date()
case'Y':
return _date.getFullYear()
case'z':
returnMath.floor((_date - newDate(_date.getFullYear(), 0, 1)) / 864e5)
case'Z':
return -_date.getTimezoneOffset() * 60
default:
thrownewError('Unrecognized _date format token')
  }
}