ARIAMixin properties should be nullable?

[h-joo]

In the ARIAMixin definition of TS 4.4-rc, the aria* properties are non-nullable, but according to the spec draft for AOM aria reflection with the AriaAttributes mixin, it seems to be nullable. Should these types need to be reconsidered to be nullable?

[orta]

Linking to microsoft/TypeScript#45571

It looks like this is defined upstream as not being nullable: https://github.com/w3c/webref/blob/master/ed/idlnames/ARIAMixin.idl - which does seem to match that spec https://www.w3.org/TR/wai-aria-1.2/#AriaAttributes

I think I agree that this is probably something we want to be classed as optional properties though, not quite decided. What does it look like to hit an error with this?

[h-joo]

We used to have Element-like interface implementation which used to have their own ariaLabel/ariaExpanded properties. The type of the two properties is string|undefined which now have problem on assignment to Element type as Element starts to extend from ARIAMixin as well with having the properties as a string type.

Sample error message:

TS2345: Argument of type 'X' is not assignable to parameter of type 'Element'.
  Types of property 'ariaExpanded' are incompatible.

[saschanaz]

• AriaAttributes properties made non-nullable by resolves #1058, enumerated values for DOMString reflection w3c/aria#1261
• AriaAttributes is renamed to AriaMixin by Generalize AccessibilityRole/AriaAttributes IDL w3c/aria#984

So, per the spec, assigning undefined is wrong and it will be converted to a string "undefined".

[jnurthen]

Note w3c/aria#1611 makes them nullable again.

[saschanaz]

Thanks, in that case it will be updated by webref within a few days.

[saschanaz]

Fixed by #1200

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