JS: the Set Object (basics)

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.

Create Set

Create a empty set.

// create a empty set
const xx = new Set();
console.log(xx);
// Set(0) {}

// add items
xx.add(8);
xx.add(4);
console.log(xx);
// Set(2) { 8, 4 }

Create a set from values in iterable object.

console.log(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. When elements are objects (or arrays), their reference identity are compared for equality, not their content.

// 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 ] }

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"));