set quickly implements union, intersection, and difference

// 并集
const union = (setA, setB) => {
  return new Set([...setA, ...setB])
}


// 交集
const intersection = (setA, setB) => {
  return new Set([...setA].filter(x => setB.has(x)))
}


//差集
const difference = (setA, setB) => {
  return new Set([...setA].filter(x => !setB.has(x)))
}