Map和Object的基本操作

1. 键值区别

Map 默认情况下，Map不包含任何键。这是一个全新的开始

Object 默认情况下，有自己的原型，包含对象的基本方法

2. map和Object的迭代

2.1 Map迭代

for (const [key, value] of map) {
  console.log(`key: ${key}, value: ${value}`);
}

for (const key of map.keys()) { // or map.values()
  console.log(key);
}

//map支持forEach方法
map.forEach((value, key) => console.log(`key: ${key}, value: ${value}`));

2.2 Object迭代

for(let key in obj){
    console.log(`key: ${key}, value: ${obj[key]}`)
}

Object.entries(obj).forEach((item) => console.log(`key: ${item[0]}, value: ${item[1]}`))

3. Map和Object与数组合并

3.1 Map与数组合并

//map转数组
Array.from(map) 或者 [...map]

//数组转map
let arr = [ [1, 'one'], [2, 'two'] ]
new Map(arr)

//map与数组合并
let map = new Map([ [1, 'one'], [2, 'two'] ]);
let arr = [3, 'three']

let combinedMap = new Map(...map, arr); 
// { 1 => 'one', 2 => 'two', 3 => 'three' }

let combinedArr = [...map, arr];
// [ [1, 'one'], [2, 'two'], [3, 'three'] ]

3.2 将对象合并到数组中

Array.from(Object.entries(obj)) 或 [...Object.entries(obj)]

3.3 Map与数组转换

let arr = ['one','two']

//数组转map
new Map(arr.map((t,i) => [i,t]))

//map转数组
Array.from(map)
Array.from(map).map(t => t[1])
Array.from(map).map(t => t[0])
Array.from(map.values())
Array.from(map.keys())
[...map]
[...map.values()]
[...map.keys()]

4. Map实现数组去重

//map的key也是不允许重复的，如果初始化时有重复，会自动删除，map和set一样可以实现去重
const books = [
    { id: 1, title: 'How To Win Friends And Influence People', author: 'Dale Carnegie' },
    { id: 1, title: 'How To Win Friends And Influence People', author: 'Dale Carnegie' },
    { id: 2, title: 'The Alchemist', author: 'Paulo Coelho' },
]

const uniqueObjsArr = [...new Map(books.map(book => [book.id, book])).values()]

5. Map的key是有序的，可以实现队列的效果

 

出处：JavaScript选择 map而非对象(object)存储键值对的 5 个理由附示例