Set

const mySet1 = new Set();

mySet1.add(1); // Set(1) { 1 }
mySet1.add(5); // Set(2) { 1, 5 }
mySet1.add(5); // Set(2) { 1, 5 }
mySet1.add(""); // Set(3) { 1, 5, '' }
const o = { a: 1, b: 2 };
mySet1.add(o);

mySet1.add({ a: 1, b: 2 }); // o    ,    

mySet1.has(1); // true
mySet1.has(3); // false,  3     
mySet1.has(5); // true
mySet1.has(Math.sqrt(25)); // true
mySet1.has("".toLowerCase()); // true
mySet1.has(o); // true

mySet1.size; // 5

mySet1.delete(5); //   5  set
mySet1.has(5); // false, 5  

mySet1.size; // 4,     

mySet1.add(5); // Set(5) { 1, "", {...}, {...}, 5 } -        ,        

console.log(mySet1); // Set(5) { 1, "", {}, {}, 5 }

for (const item of mySet1) {
  console.log(item);
}
// 1, "", { "a": 1, "b": 2 }, { "a": 1, "b": 2 }, 5

for (const item of mySet1.keys()) {
  console.log(item);
}
// 1, "", { "a": 1, "b": 2 }, { "a": 1, "b": 2 }, 5

for (const item of mySet1.values()) {
  console.log(item);
}
// 1, "", { "a": 1, "b": 2 }, { "a": 1, "b": 2 }, 5

//     
for (const [key, value] of mySet1.entries()) {
  console.log(key);
}
// 1, "", { "a": 1, "b": 2 }, { "a": 1, "b": 2 }, 5

//   Set   Array   Array.from
const myArr = Array.from(mySet1); // [1, "", {"a": 1, "b": 2}, {"a": 1, "b": 2}, 5]

//    ,     HTML-
mySet1.add(document.body);
mySet1.has(document.querySelector("body")); // true

//   Set  Array
const mySet2 = new Set([1, 2, 3, 4]);
console.log(mySet2.size); // 4
console.log([...mySet2]); // [1, 2, 3, 4]

//     
const intersection = new Set([...mySet1].filter((x) => mySet2.has(x)));

//     
const difference = new Set([...mySet1].filter((x) => !mySet2.has(x)));

//     forEach()
mySet2.forEach((value) => {
  console.log(value);
});
// 1
// 2
// 3
// 4

function isSuperset(set, subset) {
  for (const elem of subset) {
    if (!set.has(elem)) {
      return false;
    }
  }
  return true;
}

function union(setA, setB) {
  const _union = new Set(setA);
  for (const elem of setB) {
    _union.add(elem);
  }
  return _union;
}

function intersection(setA, setB) {
  const _intersection = new Set();
  for (const elem of setB) {
    if (setA.has(elem)) {
      _intersection.add(elem);
    }
  }
  return _intersection;
}

function symmetricDifference(setA, setB) {
  const _difference = new Set(setA);
  for (const elem of setB) {
    if (_difference.has(elem)) {
      _difference.delete(elem);
    } else {
      _difference.add(elem);
    }
  }
  return _difference;
}

function difference(setA, setB) {
  const _difference = new Set(setA);
  for (const elem of setB) {
    _difference.delete(elem);
  }
  return _difference;
}

// 
const setA = new Set([1, 2, 3, 4]);
const setB = new Set([2, 3]);
const setC = new Set([3, 4, 5, 6]);

isSuperset(setA, setB); // true
union(setA, setC); // Set {1, 2, 3, 4, 5, 6}
intersection(setA, setC); // Set {3, 4}
symmetricDifference(setA, setC); // Set {1, 2, 5, 6}
difference(setA, setC); // Set {1, 2}

const myArray = ["value1", "value2", "value3"];

//    Set     
const mySet = new Set(myArray);

mySet.has("value1"); // true

//   spread     .
console.log([...mySet]); //      ,   myArray

const numbers = [2, 3, 4, 4, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 5, 32, 3, 4, 5];

console.log([...new Set(numbers)]); // [2, 3, 4, 5, 6, 7, 32]

//    (   "F"  "f")
new Set("Firefox"); // Set(7) [ "F", "i", "r", "e", "f", "o", "x" ]

//   ("f"     ,       )
new Set("firefox"); // Set(6) [ "f", "i", "r", "e", "o", "x" ]

const array = Array.from(document.querySelectorAll("[id]")).map((e) => e.id);

const set = new Set(array);
console.assert(set.size === array.length);