Require exactly one key of type string

[jakeboone02]

Is there was a way to type an object to require that it has exactly one key? The key itself can be any string (or number or symbol for that matter), but I'd like to ensure there are at least and at most one non-prototype/inherited property.

The use case is for typing the JavaScript implementation of JsonLogic (npm / DT types). In the runtime code, the "logic" object itself and each nested object must satisfy the condition Object.keys(logic).length === 1 (see code).

I tried RequireExactlyOne<Record<string, any>, string>, but that seems to be effectively the same as Record<string, any>.

Upvote & Fund

• We're using Polar.sh so you can upvote and help fund this issue.
• The funding will be given to active contributors.
• Thank you in advance for helping prioritize & fund our backlog.

[sindresorhus]

Sounds useful. Not sure whether it's possible though.