Creating a UTC object from a dayjs object fails

[JuanMME]

Describe the bug
Do this:

let plainDate = '2018-02-20T23:59:59.000Z';
let obj = dayjs(plainDate);
console.log(1, dayjs.utc(plainDate).toISOString());
console.log(1, dayjs.utc(obj).toISOString());
console.log(2, dayjs(plainDate).utc().toISOString());
console.log(2, dayjs(obj).utc().toISOString());

The second console.log will print an incorrect date (today at 00:00:00) instead of the original date passed. Doing this however:

console.log(1, dayjs.utc(obj.toDate()).toISOString());

Seems to work just fine.

Expected behavior
Creating UTC Dayjs objects should work the same way as creating regular dayjs objects, which means passing a dayjs object as a parameter should work just fine. Instead, creating a dayjs object from a dayjs object works only if you do dayjs() but not dayjs.utc().

Information

• Day.js Version 1.9.6
• OS: Windows 10
• Browser Edge 87
• Time zone: CET

[iamkun]

Bug confirmed. dayjs.utc(Dayjs) should have the same behavior as dayjs(Dayjs)

[rmartins90]

Tried to reproducte this behavior in the current version and this seems to solved now. Below, you can find the test used to validate this scenario.

Wasn't able to run over all the tests to verify that this scenario is covered already. So, no PR was created, but it should be closed.

  const dayjsDate = dayjs()
  const daysjsUTCDate = dayjs.utc()

  expect(dayjsDate.toISOString()).toBe(daysjsUTCDate.toISOString())

  const plainDate = '2018-02-20T23:59:59.000Z'
  const obj = dayjs(plainDate)

  const result1 = dayjs.utc(plainDate).toISOString()
  const result2 = dayjs.utc(obj).toISOString()
  const result3 = dayjs(plainDate).utc().toISOString()
  const result4 = dayjs(obj).utc().toISOString()

  expect(result1).toEqual(result2)
  expect(result2).toEqual(result3)
  expect(result3).toEqual(result4)