sets.js

var cards = new Set()
cards.add('♠')
cards.add('♥')
cards.add('♦')
cards.add('♣')

cards.has('♠') //true

cards.has('joker') //false

cards.size //4

cards.forEach((card) => console.log(card));

/*
Would log:
♠
♥
♦
♣
*/

cards.add('♣')

cards.size // Still four as ♣ was already there in the cards set.