canched value can only be object about node-lru-cache

[isaacs]

Yes, it uses undefined as a signal in some cases to mean that the item is not found, and this will cause incorrect behavior. Don't put undefined in the cache. If you want a key to be undefined, delete it.

I suppose the set method could be changed to allow cache.set(key, undefined) to be an alias for cache.delete(key), would that be to your liking?

The downside, I guess, would be if you wanted cache.has(key) to return true?

[isaacs]

Another option would be to use a special object that means "no value here", so it would "have" the object, but still return undefined from cache.get?

[tjx666]

Yes, allow set value to be V | undefined is enough for me