Set

Set objects let you store unique values of any type, whether primitive values or object references. Value equality is not based on the same algorithm as the one used in the === operator. Specifically, for Sets, +0 (which is strictly equal to -0) and -0 are different values. NaN can also be stored in a Set.

API

Examples

var mySet = new Set();

mySet.add(1);
mySet.add(5);
mySet.add("some text");

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.size; // 3

mySet.delete(5); // removes 5 from the set
mySet.has(5);    // false, 5 has been removed

mySet.size; // 2, we just removed one value

// iterate over items in set
for (let item of mySet) console.log(item); // logs the items in the order: 1, "some text" 

// convert set to plain Array
var myArr = [v for (v of mySet)]; // [1, "some text"]

// the following will also work if run in an HTML document
mySet.add(document.body);
mySet.has(document.querySelector("body")); // true

// converting between Set and Array
mySet2 = Set([1,2,3,4]);
mySet2.size; // 4
[...mySet2]; // [1,2,3,4]

// intersect can be simulated via  Set(x for (x of set1) if (set2.has(x)))

Browser compatibility

See also

• Map and Set bug at Mozilla
• ECMAScript Harmony proposal