Whether an equivalent value exists in this collection.
This operation is very fast for sets because they are backed by a hash table.
The operation is fast for SortedSet and SortedArraySet by virtue of a binary
search.
To avoid confusion with the linear search available as has(value, equals) on
Array, List, and Deque, if you pass a second argument, this method will
throw an exception.
var set = new Set([1, 2, 3]); set.has(2); set.has(4);
Returns whether an entry with the given key exists in a Map.
Returns whether an equivalent value exists in this collection.