Set example in JS

ninja-set.js

const ninjas = new Set(['Kuma', 'Hattori', 'Yagyu']);
const samurai = new Set(['Hattori', 'Oda', 'Tomoe']);

const pureNinjas = new Set([...ninjas].filter(ninja => !samurai.has(ninja)));
const everyone = new Set([...ninjas, ...samurai]);

console.log(pureNinjas.size === 2, 'There’s only one ninja samurai');
console.log(pureNinjas.has('Kuma'), 'Kuma is a true ninja');
console.log(pureNinjas.has('Yagyu'), 'Yagyu is a true ninja');
console.log(everyone.size === 5, 'Do not count twice Hattori, the ninja samurai');