JS: the Set Object Tutorial

What is Set Object

(new in ECMAScript 2015)

A “Set” object are collections of values.

• Value can be any type.
• The values in a set are distinct. (a specific value can occur only once in a set.)
• order of values are maintained, by insertion time.

Creating Set

new Set()

Create a empty set.

new Set(iterable)

Create a set from values in iterable object iterable.

new Set([3, 4, 5])
// Set(3) { 3, 4, 5 }

• JS: Iterable Object
• JS: Set Constructor

Parent of Set Objects

The parent of any set object is Set.prototype.

• JS: Prototype and Inheritance
• JS: Set.prototype

Size of Set

• JS: Set.prototype.size

Add a Value

• JS: Set.prototype.add

Delete a Value

• JS: Set.prototype.delete

Check Existence

• JS: Set.prototype.has

Clear Set

• JS: Set.prototype.clear

Iteration

• JS: for-of Loop
• JS: Set.prototype.forEach

Union, Intersection, Difference

• JS: Set Union, Intersection, Difference 📜

Convert Set to Array

• JS: Array.from

Set of Arrays, Set of Objects

Set can contain value of any type. But when elements are objects (or arrays), be careful that two object of same structure and element values is considered different objects.

// set of arrays

// note the array [3] is duplicated, because [3] === [3] returns false
console.log(new Set([4, [3], [3]]));
// Set(3) { 4, [ 3 ], [ 3 ] }

// note here there the [3] is not duplicated
const xx = [3];
console.log(new Set([4, xx, xx]));
// Set(2) { 4, [ 3 ] }

Add Properties to Set

Because set is a object, you can add properties to it. 〔see JS: Object Type〕

const xx = new Set([4, 5, 6]);

// you can add properties to a set object
xx.pp = 3;

console.log(xx.pp === 3);
console.log(Object.hasOwn(xx, "pp"));