Map

Map 对象保存键值对，并且能够记住键的原始插入顺序。任何值（对象或者基本类型）都可以作为一个键或一个值。

//创建Map只能通过new
const myMap = new Map([
    [1, 'one'],
    [2, 'two'],
    [3, 'three'],
]);

const map1 = new Map();

map1.set('a', 1);
map1.set('b', 2);
map1.set('c', 3);
console.log(typeof map1)//object

for (const map1Element of map1) {
    console.log(map1Element)
}
//[ 'a', 1 ]
//[ 'b', 2 ]
//[ 'c', 3 ]

使用对象的设置属性方法

map1.name = 'tom'
console.log(map1)//Map(3) { 'a' => 1, 'b' => 2, 'c' => 3, name: 'tom' }
console.log(map1.has('name'))//false   
//name并未真正存到map1中，迭代或查询也找不到
for (const map1Element of map1) {
    console.log(map1Element)
}
//[ 'a', 1 ]
//[ 'b', 2 ]
//[ 'c', 3 ]

在Map上存储应该用set(key, value)方法

Map和Object对比

Set

Set对象是值的集合，你可以按照插入的顺序迭代它的元素。Set 中的元素只会出现一次，即 Set 中的元素是唯一的

//创建Set只能通过new
const mySet = new Set(['hello',1,2,true,function a(){console.a('hi!~')}])
console.log(typeof myset)//object
console.log(mySet)//Set(5) { 'hello', 1, 2, true, [Function: a] }
mySet.add("some text"); // Set [ 1, 5, "some text" ]

//迭代Set
for (const item of mySet) {
    console.log(item)
}
//hello
//1
//2
//true
//[Function: a]
//some text

// 判断两个集合是否相等
function isSuperset(set, subset) {
    for (let elem of subset) {
        if (!set.has(elem)) {
            return false;
        }
    }
    return true;
}

// Set 和 Array 互换
mySet2 = new Set([1, 2, 3, 4]);
mySet2.size;               // 4
[...mySet2];               // [1,2,3,4]

//合并两个Set
function union(setA, setB) {
    let _union = new Set(setA);
    for (let elem of setB) {
        _union.add(elem);
    }
    return _union;
}
let set1 = new Set([1,2,3,4])
let set2 = new Set([5,6,7,8])
console.log(union(set1, set2))//Set(8) { 1, 2, 3, 4, 5, 6, 7, 8 }

// 找两个Set的交集
function intersection(setA, setB) {
    let _intersection = new Set();
    for (let elem of setB) {
        if (setA.has(elem)) {
            _intersection.add(elem);
        }
    }
    return _intersection;
}
let set1 = new Set([1,2,3,4])
let set2 = new Set([3,4,5,6])
console.log(intersection(set1, set2))//Set(2) { 3, 4 }

//找两个Set的差集
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;
}
let set1 = new Set([1,2,3,4])
let set2 = new Set([3,4,5,6])
console.log(symmetricDifference(set1, set2))//Set(4) { 1, 2, 5, 6 }

//删除A中和B一样的元素
function difference(setA, setB) {
    let _difference = new Set(setA);
    for (let elem of setB) {
        _difference.delete(elem);
    }
    return _difference;
}
let set1 = new Set([1,2,3,4])
let set2 = new Set([3,4,5,6])
console.log(difference(set1, set2))//Set(2) { 1, 2 }

数组去重

const arr = [1,1,1,1,1,2,2,2,2,3,3,3,3,4,4,45,5,5,6,6]
console.log([...new Set(arr)])
[
   1, 2, 3, 4,
  45, 5, 6
]

感谢MDN写出如此优秀的内容，跟着文章敲一遍感觉非常清晰。