isDictionaryItem()function

isDictionaryItem(dict: ImmutableDictionary<T>, key: unknown): key is string
ParamType
dictImmutableDictionary<T>
The dictionary to test against. required
keyunknown
The key to test for. required
Return
key is string
true if key is a string and an own prop of dict, narrowing its type.

Is an unknown value the key for an own prop of a dictionary.