The Set object lets you store unique values of any type, whether primitive values or object references. Set objects are collections of values, you can iterate its elements in insertion order. A value in the Set may only occur once; it is unique in the Set’s collection.
Example:
var mySet = new Set(); mySet.add(1); mySet.add(5); mySet.add("some text"); var o = {a: 1, b: 2}; mySet.add(o); mySet.has(1); // true mySet.has(3); // false, 3 has not been added to the set mySet.has(5); // true mySet.has(Math.sqrt(25)); // true mySet.has("Some Text".toLowerCase()); // true mySet.has(o); // true mySet.size; // 4 mySet.delete(5); // removes 5 from the set mySet.has(5); // false, 5 has been removed mySet.size; // 3, we just removed one value