Cannot import isDayJs from the ESM output

[sybers]

Describe the bug
The following import doesn't work anymore.

import { isDayjs } from 'dayjs';

Before 1.10, the module field in package.json used to point to days.min.js which was not an ESM output. Now it is pointing to esm/index.js and the isDayjs function is not properly exported (it is only added to dayjs.isDayJs, which is later exported as the default export).

Same thing applies to locale, extend and unix functions.

Expected behavior
I'd like to be able to do:

import { isDayjs } from 'dayjs'

isDayjs(new Date());

instead of having to do:

import dayjs from 'dayjs';

dayjs.isDayjs(dayjs());

Information

• Day.js Version: 1.10.1
• OS: macOS@11.1
• Bundler: Webpack@4.41.5
• Browser: -
• Time zone: -

[iamkun]

Sorry for the inconvenience, just wondering why a 'module' entry change could lead to such a huge change?

[sybers]

Oh I see you were already discussing the same issue on #1281 after opening this ticket.

As far as I understand, this is related to how UMD exposes the default export. But I am no expert in that domain 😅

A way to solve this would be to explicitly export the above functions in the source code.

[TheThing]

Yeah, it's weird how angular/babylon/whatever is repackaging the file cause node ecmascript modules doesn't care either way regardless of the version as I reproduced in my testing and provided identical output.

Feel free to use my shitty hotfix though that I posted at the end on that issue, lol

[iamkun]

let move this discussion to #1281