zoned-date-time/src/zoned-date-time.js

A tiny JavaScript Date with full IANA timezone support

function definePrivateProperty(object, property, value) {
  Object.defineProperty(object, property, {
    value: value
  });
}

function getUntilsIndex(original, untils) {
  var index = 0;
  var originalTime = original.getTime();

  // TODO Should we do binary search for improved performance?
  while (index < untils.length - 1 && originalTime >= untils[index]) {
    index++;
  }
  return index;
}

function setWrap(fn) {
  var offset1 = this.getTimezoneOffset();
  var ret = fn();
  this.original.setTime(new Date(this.getTime()));
  var offset2 = this.getTimezoneOffset();
  if (offset2 - offset1) {
    this.original.setMinutes(this.original.getMinutes() + offset2 - offset1);
  }
  return ret;
}

var ZonedDateTime = function(date, timeZoneData) {
  definePrivateProperty(this, "original", new Date(date.getTime()));
  definePrivateProperty(this, "local", new Date(date.getTime()));
  definePrivateProperty(this, "timeZoneData", timeZoneData);
  definePrivateProperty(this, "setWrap", setWrap);
  if (!(timeZoneData.untils && timeZoneData.offsets && timeZoneData.isdsts)) {
    throw new Error("Invalid IANA data");
  }
  this.setTime(this.local.getTime() - this.getTimezoneOffset() * 60 * 1000);
};

ZonedDateTime.prototype.clone = function() {
  return new ZonedDateTime(this.original, this.timeZoneData);
};

// Date field getters.
["getFullYear", "getMonth", "getDate", "getDay", "getHours", "getMinutes",
"getSeconds", "getMilliseconds"].forEach(function(method) {
  // Corresponding UTC method, e.g., "getUTCFullYear" if method === "getFullYear".
  var utcMethod = "getUTC" + method.substr(3);
  ZonedDateTime.prototype[method] = function() {
    return this.local[utcMethod]();
  };
});

// Note: Define .valueOf = .getTime for arithmetic operations like date1 - date2.
ZonedDateTime.prototype.valueOf =
ZonedDateTime.prototype.getTime = function() {
  return this.local.getTime() + this.getTimezoneOffset() * 60 * 1000;
};

ZonedDateTime.prototype.getTimezoneOffset = function() {
  var index = getUntilsIndex(this.original, this.timeZoneData.untils);
  return this.timeZoneData.offsets[index];
};

// Date field setters.
["setFullYear", "setMonth", "setDate", "setHours", "setMinutes", "setSeconds", "setMilliseconds"].forEach(function(method) {
  // Corresponding UTC method, e.g., "setUTCFullYear" if method === "setFullYear".
  var utcMethod = "setUTC" + method.substr(3);
  ZonedDateTime.prototype[method] = function(value) {
    var local = this.local;
    // Note setWrap is needed for seconds and milliseconds just because
    // abs(value) could be >= a minute.
    return this.setWrap(function() {
      return local[utcMethod](value);
    });
  };
});

ZonedDateTime.prototype.setTime = function(time) {
  return this.local.setTime(time);
};

ZonedDateTime.prototype.isDST = function() {
  var index = getUntilsIndex(this.original, this.timeZoneData.untils);
  return Boolean(this.timeZoneData.isdsts[index]);
};

ZonedDateTime.prototype.inspect = function() {
  var index = getUntilsIndex(this.original, this.timeZoneData.untils);
  var abbrs = this.timeZoneData.abbrs;
  return this.local.toISOString().replace(/Z$/, "") + " " +
    (abbrs && abbrs[index] + " " || (this.getTimezoneOffset() * -1) + " ") +
    (this.isDST() ? "(daylight savings)" : "");
};

ZonedDateTime.prototype.toDate = function() {
  return new Date(this.getTime());
};

// Type cast getters.
["toISOString", "toJSON", "toUTCString"].forEach(function(method) {
  ZonedDateTime.prototype[method] = function() {
    return this.toDate()[method]();
  };
});

if (typeof module !== "undefined" && module.exports) {
  module.exports = ZonedDateTime;
}