Stepping through days is not correct for Asia/Beirut.

[hifall]

Description of the Issue and Steps to Reproduce:

I am seeing some strange behavior while using moment to step through each day between a moment range in timezone Asia/Beirut. I have created a minimal test case to demonstrate this behavior:

const moment = require('moment-timezone');

const tzStart = moment("2015-03-27T19:21:24.000Z").tz('Asia/Beirut');
const tzEnd = moment("2015-03-30T19:21:24.000Z").tz('Asia/Beirut');
var startOfDay = tzStart.clone();
var endOfDay = tzStart.clone();
endOfDay.endOf('day');
console.log('startOfDay: ' + startOfDay.format());
console.log('endOfDay: ' + endOfDay.format());
while (endOfDay.isBefore(tzEnd)) {
    console.log('     ');

    // Move to next day.
    startOfDay.add(1, 'days').startOf('day');
    endOfDay.add(1, 'days');
    console.log('startOfDay: ' + startOfDay.format());
    console.log('endOfDay: ' + endOfDay.format());
}

Please include the values of all variables used.

The above script produces:

startOfDay: 2015-03-27T21:21:24+02:00
endOfDay: 2015-03-27T23:59:59+02:00

startOfDay: 2015-03-28T00:00:00+02:00
endOfDay: 2015-03-28T23:59:59+02:00

startOfDay: 2015-03-28T00:00:00+02:00
endOfDay: 2015-03-29T23:59:59+03:00

startOfDay: 2015-03-28T00:00:00+02:00
endOfDay: 2015-03-30T23:59:59+03:00

This doesn't seem correct to me, as startOfDay in last 2 groups (in bold) stay on 2015-03-28, rather than moving to the next day.

If I change the timezone to another one like Asia/Shanghai, it produces:

startOfDay: 2015-03-28T03:21:24+08:00
endOfDay: 2015-03-28T23:59:59+08:00

startOfDay: 2015-03-29T00:00:00+08:00
endOfDay: 2015-03-29T23:59:59+08:00

startOfDay: 2015-03-30T00:00:00+08:00
endOfDay: 2015-03-30T23:59:59+08:00

startOfDay: 2015-03-31T00:00:00+08:00
endOfDay: 2015-03-31T23:59:59+08:00

Which is correct.

Environment:

Node.JS v6.10.3 on Ubuntu 16.0.4

Other information that may be helpful:

• The time zone setting of the machine the code is running on: UTC
• The time and date at which the code was run: Fri Sep 1 12:10:09 UTC 2017
• Other libraries in use: moment-timezone

If you are reporting an issue, please run the following code in the environment you are using and include the output:

console.log( (new Date()).toString())
console.log((new Date()).toLocaleString())
console.log( (new Date()).getTimezoneOffset())
console.log(moment.version)

Fri Sep 01 2017 12:11:55 GMT+0000 (UTC)
9/1/2017, 12:11:55 PM
0
2.16.0

[sirxemic]

https://timezonedb.com/time-zones/Asia/Beirut

2015-03-29 there starts at 1am, not 12am. Basically when you add 1 day to 2015-03-28T00:00:00+02:00 it becomes 2015-03-28T23:00:00+02:00 in moment.js.

You may want to do something like

const moment = require('moment-timezone');

const tzStart = moment("2015-03-27T19:21:24.000Z").tz('Asia/Beirut');
const tzEnd = moment("2015-03-30T19:21:24.000Z").tz('Asia/Beirut');

const iterator = tzStart.clone().hour(12);
const end = tzEnd.clone().hour(12);

console.log('startOfDay: ' + iterator.clone().startOf('day').format());
console.log('endOfDay: ' + iterator.clone().endOf('day').format());

while (iterator <= end) {
    console.log('     ');

    // Move to next day.
    iterator.add(1, 'days')
    console.log('startOfDay: ' + iterator.clone().startOf('day').format());
    console.log('endOfDay: ' + iterator.clone().endOf('day').format());
}

output:

startOfDay: 2015-03-27T00:00:00+02:00
endOfDay: 2015-03-27T23:59:59+02:00

startOfDay: 2015-03-28T00:00:00+02:00
endOfDay: 2015-03-28T22:59:59+02:00

startOfDay: 2015-03-29T01:00:00+03:00
endOfDay: 2015-03-30T00:59:59+03:00

startOfDay: 2015-03-30T00:00:00+03:00
endOfDay: 2015-03-30T23:59:59+03:00

startOfDay: 2015-03-31T00:00:00+03:00
endOfDay: 2015-03-31T23:59:59+03:00

...but as you can see it says 2015-03-30T00:59:59+03:00 is the end of 2015-03-29 ... which doesn't seem to be correct either...

In any case, having DST taking place at 12am is what's causing trouble here.

[hifall]

@sirxemic, thanks for pointing that out.

Our app depends on stepping through days like this, so this causes our app to break.

[mattjohnsonpint]

Yes, there are multiple open bugs related to startOf and endOf not working correctly with time zones. I believe #3132 explains at least part of this. To simplify the bug, note the following:

moment.tz("2015-03-28T00:00:00+02:00", "Asia/Beirut").add(1, 'day').startOf('day').format()
//=> "2015-03-28T00:00:00+02:00" should be "2015-03-29T01:00:00+03:00"

moment.tz("2015-03-28T01:00:00+03:00", "Asia/Beirut").add(1, 'day').endOf('day').format()
//=> "2015-03-28T22:59:59+02:00" should be "2015-03-29T23:59:59+02:00"

To work around this bug:

moment.tz("2015-03-28T00:00:00+02:00", "Asia/Beirut").hour(12).add(1, 'day').startOf('day').format()
//=> "2015-03-29T01:00:00+03:00"

moment.tz("2015-03-28T01:00:00+03:00", "Asia/Beirut").hour(12).add(2, 'days').startOf('day').subtract(1, 'ms').format()
//=> "2015-03-29T23:59:59+03:00"

In your case, adjust your sample code as follows:

const tzStart = moment("2015-03-27T19:21:24.000Z").tz('Asia/Beirut');
const tzEnd = moment("2015-03-30T19:21:24.000Z").tz('Asia/Beirut');

const startOfDay = tzStart.clone().startOf('day');
const endOfDay = tzStart.clone().hour(12).add(1, 'day').startOf('day').subtract(1, 'ms');

while (endOfDay.isBefore(tzEnd)) {
    console.log('startOfDay: ' + startOfDay.format());
    console.log('endOfDay: ' + endOfDay.format());
    console.log('     ');

    // Move to next day.
    startOfDay.hour(12).add(1, 'days').startOf('day');
    endOfDay.hour(12).add(2, 'days').startOf('day').subtract(1, 'ms');
}

[hifall]

@mj1856, thanks for your workaround. After the workaround is applied, our internal test that was broken is not reporting the issue.

Although many other of our tests are still broken, which I might file GitHub issues on later.

[hifall]

I found that there is no test cases covering such scenarios in either moment's repo or moment-timezone's repo. I think at least there should be some tests to cover all supported timezones.

[icambron]

@mj1856 Is this a bug in Moment or moment-timezone (or, possibly a combination)? I'm wondering if it needs to be moved to other repository?