Additional UnknownRecord.is check for undefined added

[mlegenhausen]

This PR introduces an additional check for the undefined value to UnknownRecord.is. Background is that we at Unsplash experience a "small" amount of Chrome users where Object.prototype.toString.call(undefined) returns [object Window] instead of [object Undefined].

We weren't able to reproduce this error on our side, but are in the process of rolling out a patch to all users.

[gcanti]

@mlegenhausen what do you think about #611 (comment)?

[mlegenhausen]

Sounds interesting, still does not explain why the string representation of undefined is sometimes different but it seems we can not rely on Object.prototype.toString at all.

On first sight u !== null && typeof u === 'object' && !Array.isArray(u) seems to be a valid replacement.

If you want I can change my PR accordantly?

[gcanti]

If you want I can change my PR accordantly?

Yeah, looks like we can kill two birds with one stone

[mlegenhausen]

Of cause to good to be true that this a drop in replacement 😉 this has false positives for new Number(), new Boolean() and so on.

[mlegenhausen]

Looking at the PR 231b9f5 it seems in a previous version new Number was a valid UnknownRecord then it was changed to being invalid. Should we move this case again to being valid?

[gcanti]

Should we move this case again to being valid?

IMO yes, the goal of that PR was to not allow arrays but ended up disallowing more Record<string, unknown> candidates

[mlegenhausen]

@gcanti ready for review.

[gcanti]

Thank you @mlegenhausen, patch released