A frightening monkey-patch for the Safari Date constructor to construct dates using ISO strings without applying the timezone offset.

safariDate.js

(function (w) {
  // latest versions of Safari will have an Apple Pay object
  if (!w.ApplePaySession) {
    return;
  }

  var _Date = window.Date;
  var unbind = Function.bind.bind(Function.bind);

  function instantiate(constructor, args) {
    return new (unbind(constructor, null).apply(null, args));
  }

  w.Date = function(Date) {
    NewDate.prototype = Date.prototype;
    NewDate.now = Date.now;
    NewDate.UTC = Date.UTC;
    NewDate.parse = Date.parse;

    return NewDate;

    function NewDate() {
      if (arguments.length === 1 && typeof arguments[0] === 'string') {
        // validate ISO'ish formats that PestPac uses:
        // `2000-01-01 12:34:56`, `2000-01-01T12:34:56`, `2000-01-01 12:34`, `2000-01-01T12:34`
        var rgx = /(\d{4}-[01]\d-[0-3]\dT[0-2]\d:[0-5]\d:[0-5]\d\.\d+)|(\d{4}-[01]\d-[0-3]\d[T| ]{1}[0-2]\d:[0-5]\d:[0-5]\d)$|(\d{4}-[01]\d-[0-3]\dT[0-2]\d:[0-5]\d)$/i;

        var results = arguments[0].match(rgx);

        if (results) {
          // for testing: remove this line after testing
          console.log('YAHTZEE!!');
          var dateString = results[0].replace(' ', 'T');
          var parts = dateString.toUpperCase().split('T');
          var datePart = parts[0];
          var timePart = parts[1];
          var datePieces = datePart.split('-');
          var timePieces = timePart.split(':');

          return new Date(
            parseInt(datePieces[0]),
            parseInt(datePieces[1]) - 1, // month is a zero-based index
            parseInt(datePieces[2]),
            parseInt(timePieces[0]),
            parseInt(timePieces[1]),
            parseInt(timePieces[2] || 0)
          );
        }
      }

      return instantiate(Date, arguments);
    }
  }(_Date);
}(window));