Question

如何浅析ES6 Map或Set对象？

我想获得一个具有相同键和值的新Map或Set。

Answer 1

使用构造函数克隆地图和集：

var clonedMap = new Map(originalMap)

var clonedSet = new Set(originalSet)

Answer 2

通过for循环创建新Set的过程比Set构造函数要快。尽管程度较小，但Maps也是这样。

public void onComplete(@NonNull Task<QuerySnapshot> task) {
    if (task.isSuccessful()) {
        QuerySnapshot querySnapshot = task.getResult();
        if (querySnapshot.isEmpty()) {
            // put code here to deal with no documents in the result
        }
        else {
            // put code here to deal with documents present in the result
            for (QueryDocumentSnapshot document : querySnapshot) {
            }
        }
    }
}

Answer 3

浅克隆：

var clonedMap = new Map(originalMap)

var clonedSet = new Set(originalSet)

深度克隆：

var deepClonedMap = new Map(JSON.parse(JSON.stringify([...originalMap])))
var deepClonedSet = new Set(JSON.parse(JSON.stringify([...originalSet])))

let originalMap = new Map()
let data = {a:'a',b:'b'}
originalMap.set(1,data)

let shallowCloned = new Map(originalMap)
let deepCloned = new Map(JSON.parse(JSON.stringify([...originalMap])))
data.a = 'p'
console.log('originalMap:',[...originalMap])
console.log('shallowCloned:',[...shallowCloned])
console.log('deepCloned:',[...deepCloned])

Answer 4

我需要复制（“克隆”）一个 JavaScript 集，这个问题激起了我对克隆副本完整性的兴趣，以及这些副本来源的扰动。

测试

var fruit = new Set(['apples', 'bananas']);
var provinces = new Set(['british columbia', 'nova scotia']);
console.log('fruit:', fruit)
console.log('provinces:', provinces)
// fruit: Set [ "apples", "bananas" ]
// provinces: Set [ "british columbia", "nova scotia" ]

// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set#implementing_basic_set_operations
function unionSets(setA, setB) {
    let _union = new Set(setA);
    for (let elem of setB) {
        _union.add(elem)
    }
    return _union;
}

myUnionSet = unionSets(fruit, provinces);
console.log('myUnionSet:', myUnionSet)
// myUnionSet: Set(4) [ "apples", "bananas", "british columbia", "nova scotia" ]

// Tests:
fruit.delete('apples');
provinces.delete('british columbia');

console.log('fruit:', fruit)
console.log('provinces:', provinces)
console.log('myUnionSet:', myUnionSet)
// fruit: Set [ "bananas" ]
// provinces: Set [ "nova scotia" ]
// myUnionSet: Set(4) [ "apples", "bananas", "british columbia", "nova scotia" ]

Answer 5

如果 Map 包含非嵌套结构（例如 Map of Arrays），这里有一个快速的方法来深度复制它，对于任何感兴趣的人：

const newMap = new Map();
old.forEach((val, key) => newMap.set(key, [...old.get(key)]));

浅克隆ES6地图或集

5 个答案: