ES6 Data Structures

ES6 adds two useful and efficient data structures, Set and Map.

Set

Set is a collection of unique values of any type. It can be initialized empty or with an existing list of items.

Map

Map is key-value map. It can be initialized empty or with an existing array of array. In a Map key and value can be of any type.

WeakSet and WeakMap

WeakSet is a collection Objects.
WeakMap is a key-value map with Objects as keys.
In both of these, References to Objects are weak. So they can be garbage collected, if there is no other reference.