dayjs.utc() dropped timezone offset support

[jeiea]

Describe the bug
dayjs.utc('2020-12-01T09:00:00+0900').toDate().getTime() === new Date('2020-12-01T09:00:00+0900').getTime()

Expected behavior
The above evaluates to true. It's the behaviour of dayjs 1.8.33.

Actual behaviour

> dayjs.utc('2020-12-01T09:00:00+0900').toDate()
2020-12-01T09:00:00.090Z
> new Date('2020-12-01T00:00:00+0900')
2020-11-30T15:00:00.000Z

Information

• Day.js Version: 1.9.6
• OS: macOS
• Browser:
• Time zone: GMT+0900 (Korean Standard Time)

[iamkun]

dayjs.utc('2020-12-01T09:00:00+0900').toDate().getTime() 
   === new Date('2020-12-01T09:00:00+0900').getTime()
   === dayjs('2020-12-01T09:00:00+0900').toDate().getTime() 

The above three should have the same result. Cause it represents the same time '2020-12-01T09:00:00+0900'

[jeiea]

There was my mistake in the code snippet. I'll explain again.

What I said is your invariant is not established. codesandbox
Interestingly, all of them have different result.

// Windows 10 + Chrome 86.0.4240.198
dayjs.utc('2020-12-01T09:00:00+0900').toDate().getTime(): 1606813200090
dayjs    ('2020-12-01T09:00:00+0900').toDate().getTime(): 1606780800090
 new Date('2020-12-01T09:00:00+0900')         .getTime(): 1606780800000

[iamkun]

This might be a bug in UTC plugin.

[t-mangoe]

Hi. I researched about this issue.
In the case of '2020-12-01T09:00:00+0900', +0900 is interpreted as a value of miliseconds.
I checked regex constant to parse date string, and it may be wrong that dot character is not escaped.

dayjs/src/constant.js

Lines 28 to 29 in 17221ec

	// regex
	export const REGEX_PARSE = /^(\d{4})[-/]?(\d{1,2})?[-/]?(\d{0,2})[^0-9]*(\d{1,2})?:?(\d{1,2})?:?(\d{1,2})?.?(\d+)?$/

[bcurtin144]

@t-mangoe is correct. To be sure the last digit token in REGEX_PARSE only matches for milliseconds, the period must be escaped. Otherwise, it acts as a wildcard.

To offer some more examples, all of these are the same date/time using different ISO 8601 time zone formats:
dayjs("2020-12-31T18:00:00.000-0500")
dayjs("2020-12-31T18:00:00-05:00")
dayjs("2020-12-31T18:00:00-0500")
The first two parse correctly because REGEX_PARSE doesn't match. But the last example does match REGEX_PARSE, with the - character matching the wildcard. So the date is parsed in local time and the first three characters of 0500 become 50ms.

I'm sorry I don't know how to contribute the fix, but the code should read:
export const REGEX_PARSE = /^(\d{4})[-/]?(\d{1,2})?[-/]?(\d{0,2})[^0-9]*(\d{1,2})?:?(\d{1,2})?:?(\d{1,2})?\.?(\d+)?$/

Thank you for the library. It's very useful!

[bcurtin144]

I added a pull request with the change: #1295

[iamkun]

fixed in #1295