CalendarApp: Time Zone Ridiculous Behavior

Question 1

I understand it makes you angry (or nervous) but I guess there is no mistery in this error, just a simple misunderstanding of the calendar timezone settings.

You mentioned you tested this code extensively but I'm pretty sure you tested it on a period without daylight saving shift ..?

It appears that you defined your timezone using "GMT-0500" which seemed to be a good idea but in a few days we will be in summer time and this offset won't be the same anymore and the event that happen after the switching date are now out of date because of this change.

The solution is simple, use the timezone string as shown below, this parameter will take the hour value in the date object into account and adapt its value automatically based on summer/winter time.

This should be fairly easy to implement in your code.

replace "GMT-0500" with Session.getScriptTimeZone()

for a full explanation on this issue see this other recent post where I explain the different solutions.

Note also that the other answers forgot one small detail : the code is executed on Google's server, not in our browser, so the idea that a date is created in the timezone setting of the computer where it is created can be ambiguous... would it be our computer or Google's one ? good question ! A few years ago I spent a lot of time on this question, the former (and closed) Google help forum was full of posts on that subject because the Session.getScriptTimeZone() didn't exist at that time and it made me nervous too ^^...

Question 2

Not an answer, just a more convenient way to discuss things. You probably know all of the following, but just to make sure…

If you create a Date object in a location, the Date constructor will automatically take into account the local time zone offset. So if I'm at UTC+1000 and create a Date object for 2014-03-27, it will be created for 2014-03-27T00:00:00+1000 (i.e. for my time zone) and the time value of the Date object will be equivalent to 2014-03-26 14:00:00Z, i.e. the equivalent UTC moment, and have a time zone offset of -600 (note that toISOString uses UTC).

var date = new Date(2014, 2, 27);
// toISOString uses UTC
console.log(date.toISOString());  // 2014-03-26T14:00:00.000Z

// Get the time value to pass around
var timeValue = date.getTime();
// or just 
var timeValue = +date;

That moment can be represented in any time zone using UTC methods. For say UTC+0500, you can do:

// Create a Date object
var d = new Date(timeValue);

This Date object will have an offset for the current time zone, but that can be ignored by just using UTC methods:

// Add 5 hours to set the UTC time to the equivalent of UTC+0500
d.setUTCHours(d.getUTCHours() + 5);

// Format for output - 2014-03-26T19:00:00+0500
console.log(d.getUTCFullYear() + '-' + pad(d.getUTCMonth()+1) + '-' + pad(d.getUTCDate()) + 'T' + 
            pad(d.getUTCHours()) + ':' + pad(d.getUTCMinutes()) + ':' + pad(d.getUTCSeconds())
            + '+0500'
);

// Helper for padding
function pad(n){return (n<10?'0':'')+n;}

You probably need a function to format the output for any particular time zone offset using the above. There are also functions available that make a pretty good guess at a users' system's current time zone based on interrogating the result of generating a couple of Date objects so you can get information on daylight saving too.

I hope that helps. :-)

Oh, here's a function for presenting a Date in any time zone:

// Offset is a string in standard ISO offset format
// e.g. '+1000' is UTC+1000, '-0530' is UTC-0530
function toOffsetISOString(d, offset) {

  function pad(n) {return (n<10?  '0' : '') + n;}
  function padd(n){return (n<100? '0' : '') + pad(n);}

  d = new Date(+d);

  var sign = offset < 0? '-':'+';
  var s    = sign == '-'? -1 : 1;
  oset     = Math.abs(offset);

  var hrs = (oset/100 | 0);
  var min = oset % 100;

  d.setUTCHours(d.getUTCHours() + s*hrs, d.getUTCMinutes() + s*min);

  return d.getUTCFullYear() + '-' + pad(d.getUTCMonth()+1) + '-' + pad(d.getUTCDate()) + 'T' + 
                pad(d.getUTCHours()) + ':' + pad(d.getUTCMinutes()) + ':' + pad(d.getUTCSeconds())
                + '.' + padd(d.getUTCMilliseconds()) + offset;
}

var d = new Date();
console.log(d.toISOString() + '\n  ' + toOffsetISOString(d, '+0515'));