Set

const mySet1 = new Set()

mySet1.add(1)           // Set [ 1 ]
mySet1.add(5)           // Set [ 1, 5 ]
mySet1.add(5)           // Set [ 1, 5 ]
mySet1.add('some text') // Set [ 1, 5, 'some text' ]
const o = {a: 1, b: 2}
mySet1.add(o)

mySet1.add({a: 1, b: 2})   // o is referencing a different object, so this is okay

mySet1.has(1)              // true
mySet1.has(3)              // false, since 3 has not been added to the set
mySet1.has(5)              // true
mySet1.has(Math.sqrt(25))  // true
mySet1.has('Some Text'.toLowerCase()) // true
mySet1.has(o)       // true

mySet1.size         // 5

mySet1.delete(5)    // removes 5 from the set
mySet1.has(5)       // false, 5 has been removed

mySet1.size         // 4, since we just removed one value

console.log(mySet1)
// logs Set(4) [ 1, "some text", {…}, {…} ] in Firefox
// logs Set(4) { 1, "some text", {…}, {…} } in Chrome

// iterate over items in set
// logs the items in the order: 1, "some text", {"a": 1, "b": 2}, {"a": 1, "b": 2}
for (let item of mySet1) console.log(item)

// logs the items in the order: 1, "some text", {"a": 1, "b": 2}, {"a": 1, "b": 2}
for (let item of mySet1.keys()) console.log(item)

// logs the items in the order: 1, "some text", {"a": 1, "b": 2}, {"a": 1, "b": 2}
for (let item of mySet1.values()) console.log(item)

// logs the items in the order: 1, "some text", {"a": 1, "b": 2}, {"a": 1, "b": 2}
// (key and value are the same here)
for (let [key, value] of mySet1.entries()) console.log(key)

// convert Set object to an Array object, with Array.from
const myArr = Array.from(mySet1) // [1, "some text", {"a": 1, "b": 2}, {"a": 1, "b": 2}]

// the following will also work if run in an HTML document
mySet1.add(document.body)
mySet1.has(document.querySelector('body')) // true

// converting between Set and Array
const mySet2 = new Set([1, 2, 3, 4])
mySet2.size                    // 4
[...mySet2]                    // [1, 2, 3, 4]

// intersect can be simulated via
const intersection = new Set([...mySet1].filter(x => mySet2.has(x)))

// difference can be simulated via
const difference = new Set([...mySet1].filter(x => !mySet2.has(x)))

// Iterate set entries with forEach()
mySet1.forEach(function(value) {
  console.log(value)
})

// 1
// 2
// 3
// 4

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

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

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

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

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

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

let myArray = ['value1', 'value2', 'value3']

// Use the regular Set constructor to transform an Array into a Set
let mySet = new Set(myArray)

mySet.has('value1')     // returns true

// Use the spread operator to transform a set into an Array.
console.log([...mySet]) // Will show you exactly the same Array as myArray

// Use to remove duplicate elements from the array

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]

let text = 'India'

const mySet = new Set(text)  // Set(5) {'I', 'n', 'd', 'i', 'a'}
mySet.size  // 5

//case sensitive & duplicate omission
new Set("Firefox")  // Set(7) { "F", "i", "r", "e", "f", "o", "x" }
new Set("firefox")  // Set(6) { "f", "i", "r", "e", "o", "x" }

const array = Array
  .from(document.querySelectorAll('[id]'))
  .map(function(e) {
      return e.id
  });

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