Check if a key exists. The key can be any
JavaScript value, though the answer will always be false for keys that
cannot be found in this map
Parameters
key: K
Returns boolean
init
init:((key, value) => void)
Type declaration
(key, value): void
Initialize the key only if it
doesn't already exist. The key must be one allowed by this store. For
example a scalar store only allows primitives and remotables.
Remove the key. Throws if not found.