Adding months to date across DST does not preserve hour

[JBaczuk]

Describe the bug
If you add months to a date across DST, it does not preserve the hour as stated in the docs:

There are also special considerations to keep in mind when adding time that crosses over daylight saving time. If you are adding years, months, weeks, or days, the original hour will always match the added hour.

To Reproduce
Steps to reproduce the behavior:

> date = new Date()
2021-02-04T16:37:37.790Z
> moment(date).add(6, 'months').toISOString()
'2021-08-04T15:37:37.790Z'

Expected behavior

> date = new Date()
2021-02-04T16:37:37.790Z
> moment(date).add(6, 'months').toISOString()
'2021-08-04T16:37:37.790Z'

Screenshots
If applicable, add screenshots to help explain your problem.

Desktop (please complete the following information):

• OS: MacOS 11.2
• Node: v14.15.4
• Moment Version: 2.29.1

Moment-specific environment

• The time zone setting of the machine the code is running on: America/Denver
• The time and date at which the code was run: 1612456862588
• Other libraries in use (TypeScript, Immutable.js, etc): n/a

Please run the following code in your environment and include the output:

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

Result:

> console.log((new Date()).toString())
Thu Feb 04 2021 09:42:43 GMT-0700 (Mountain Standard Time)
> console.log((new Date()).toLocaleString())
2/4/2021, 9:42:43 AM
> console.log((new Date()).getTimezoneOffset())
420
> console.log(navigator.userAgent)
Uncaught ReferenceError: navigator is not defined
> console.log(moment.version)
2.29.1

[benzispawn]

I don't this issue on the 2.24.0
To Reproduce
`> date = new Date()
2021-02-17T15:37:07.718Z

moment(date).add(6, 'months').toISOString()
'2021-08-17T15:37:07.718Z'`

Result:
`> console.log((new Date()).toString())
Wed Feb 17 2021 12:35:22 GMT-0300 (Brasilia Standard Time)
undefined

console.log((new Date()).toLocaleString())
e()).getTimezoneOffset())
console.log(navigator.us2/17/2021, 12:35:22 PM
undefined
console.log((new Date()).getTimezoneOffset())
180
undefined
console.log(navigator.userAgent)
Mozilla/5.0 (Macintosh; Intel Mac OS X 10_6_7) AppleWebKit/534.36 (KHTML, like Gecko) NodeJS/v0.4.7 Chrome/13.0.767.0 Safari/534.36
undefined
console.log(moment.version)
2.24.0`

[benzispawn]

I don't see the problem on 2.29.1 either
`> date = new Date()
2021-02-17T15:39:26.660Z

moment(date).add(6, 'months').toISOString()
'2021-08-17T15:39:26.660Z'
console.log((new Date()).toString())
Wed Feb 17 2021 12:39:46 GMT-0300 (Brasilia Standard Time)
undefined
console.log((new Date()).toLocaleString())
2/17/2021, 12:39:46 PM
undefined
console.log((new Date()).getTimezoneOffset())
180
undefined
console.log(navigator.userAgent)
Mozilla/5.0 (Macintosh; Intel Mac OS X 10_6_7) AppleWebKit/534.36 (KHTML, like Gecko) NodeJS/v0.4.7 Chrome/13.0.767.0 Safari/534.36
undefined
console.log(moment.version)
2.29.1`

[JBaczuk]

@benzispawn I think you are running it in your local time (Brasilia Standard Time) which does not observe daylight savings, correct? Therefore, you most likely wouldn't see this issue.

The important detail in the original ticket is that it was run in America/Denver timezone which does currently observe daylight savings.

[JBaczuk]

@marwahaha Why was this closed?

[jsimpson]

We are currently experiencing the same problem.