Wrong behaviour of isBefore when using timezones

[colq2]

Describe the bug
Comparing two dayjs instances in a specific timezone wich are 1 minute apart a before each other.

var d1 = dayjs().tz('Europe/Berlin').year(2023).month(3).date(10).hour(0).minute(0).second(0).millisecond(0)
var d2 = d1.subtract(1, 'minute')
d1.isBefore(d2)
> true
d2.isBefore(d1)
> true

This is not happening when you are not using a timezone:

var d1 = dayjs().year(2023).month(3).date(10).hour(0).minute(0).second(0).millisecond(0)
var d2 = d1.subtract(1, 'minute')
d1.isBefore(d2)
> false
d2.isBefore(d1)
> true

Expected behavior
The later instance should return false when using isBefore.

Information

• Day.js Version v1.11.5
• OS: macOS
• Browser Chrome 108.0.5359.124
• Time zone: GMT+0200

[addiebarron]

Having a similar issue when testing dates across a DST boundary. Here's an example:

d1 = dayjs.tz("2022-11-06T06:40:00.000Z", "America/Los_Angeles");
d2 = dayjs.tz("2022-11-06T07:10:00.000Z", "America/Los_Angeles");
d1.isBefore(d2)
> true
d2.isBefore(d1)
> true

[KronosDev-Pro]

Hi @addiebarron, @colq2 👋

On all plugin/timezone issues, most of the time the solution is to set the date before setting the timezone and then manipulate the date (add, subtract, ...).

Another solution, more for the example of @addiebarron, the pull requests #2118 solves a number of problems on the plugin/timezone.

dayjs.tz('2023-02-10T00:00:00.000Z', 'Europe/Berlin')
// or
dayjs(new Date(2023, 2, 10)).tz('Europe/Berlin')
// or
dayjs()
    .year(2023).month(3)
    .date(10)
    .hour(0)
    .minute(0)
    .second(0)
    .millisecond(0)
    .tz('Europe/Berlin')

Hopefully this will solve your question, if so, don't forget to close this issue 😉

Tests

if you want the tests

describe('issue 2182 - after timezone set', () => {
  // colq2 e.g.
  const d1 = dayjs().tz('Europe/Berlin')
    .year(2023).month(3)
    .date(10)
    .hour(0)
    .minute(0)
    .second(0)
    .millisecond(0)
  const d2 = d1.subtract(1, 'minute')

  it('sould d2 be before d1', () => {
    expect(d2.isBefore(d1)).toBe(true)
    expect(d1.isBefore(d2)).toBe(false)
  }) // failed

  // const d1s = dayjs(new Date(2023, 2, 10)).tz('Europe/Berlin')
  const d1s = dayjs.tz('2023-02-10T00:00:00.000Z', 'Europe/Berlin')
  const d2s = d1s.subtract(1, 'minute')

  it('sould d2 be before d1, solve ?', () => {
    expect(d2s.isBefore(d1s)).toBe(true)
    expect(d1s.isBefore(d2s)).toBe(false)
  }) // passed

  // addiebarron e.g.
  const d1a = dayjs.tz('2022-11-06T06:40:00.000Z', 'America/Los_Angeles')
  const d2a = dayjs.tz('2022-11-06T07:10:00.000Z', 'America/Los_Angeles')

  it('sould d2 be before d1', () => {
    expect(d1a.isBefore(d2a)).toBe(true)
    expect(d2a.isBefore(d1a)).toBe(false)
  }) // failed on dev, but passed on pr/2118

  const d1as = dayjs(new Date(2022, 11, 6, 6, 40)).tz('America/Los_Angeles')
  const d2as = dayjs(new Date(2022, 11, 6, 7, 10)).tz('America/Los_Angeles')

  it('sould d2 be before d1, solve ?', () => {
    expect(d1as.isBefore(d2as)).toBe(true)
    expect(d2as.isBefore(d1as)).toBe(false)
  }) // passed
})

On dev branch:

On pr/2118 branch: