Test if a container holds an entry with the given key.
(c: Container, k: Key) => Void.
- The value must actually be deleted, not set to
undefinedif possible. Arrays become sparse if a value in their midst is deleted.
No implementation provided for String since String is read only. No implementation for Array since has() disregards sparse slots in arrays (so a delete op would be the same as assign(myArray, idx, undefined)) which would be inconsistent.