map存儲(chǔ)的是一個(gè)個(gè)的鍵值對(duì)。主要特性介紹如下：

1 獲取map

• 構(gòu)造函數(shù)+set方法

let mapList = new Map();
mapList.set('name','zhangsan');
console.log(mapList);//{"name" => "zhangsan"}

• 構(gòu)造函數(shù)初始化方法 傳入一個(gè)特殊的二維數(shù)組

let mapList = new Map(
[['name','zhangsan'],
['age',18]]
);
console.log(mapList );//{"name" => "zhangsan", "age" => 18}

需要注意的是內(nèi)層數(shù)組元素個(gè)數(shù)都為2，映射為一個(gè)鍵值對(duì)，超過(guò)2個(gè)會(huì)被忽略，1個(gè)會(huì)認(rèn)為該鍵值對(duì)值為undefiend "name" => undefined，0個(gè)會(huì)認(rèn)為該鍵值對(duì)鍵與值均為undefiend undefined => undefined

2 map的長(zhǎng)度size

let mapList = new Map(
[['name','zhangsan'],
['age',18]]
);
console.log(mapList.size);//2

3 map的增刪改查操作

• 增 set方法設(shè)置不存在的鍵時(shí)即為增

let mapList = new Map(
[['name','zhangsan'],
['age',18]]
);
mapList.set('count',90);
console.log(mapList);
//{"name" => "zhangsan", "age" => 18, "count" => 90}

• 刪 mapList.delete(key),mapList.clear()

let mapList = new Map(
[['name','zhangsan'],
['age',18]]
);
mapList.delete('count');
console.log(mapList);
//{"name" => "zhangsan", "age" => 18}
mapList.clear();
console.log(mapList);
//{}

• 改 mapList.set(key)設(shè)置已有鍵key時(shí)即為更改

let mapList = new Map(
[['name','zhangsan'],
['age',18]]
);
mapList.set('name','lisi');
console.log(mapList);
//{"name" => "lisi", "age" => 18}

• 查 mapList.get(key)即獲取對(duì)應(yīng)鍵的值，mapList.has(key)即判斷有無(wú)該鍵key

let mapList = new Map(
[['name','zhangsan'],
['age',18]]
);
console.log(mapList.has('name'));//true
console.log(mapList.get('name'));//zhangsan

4 遍歷

• let .. of

let mapList = new Map(
[['name','zhangsan'],
['age',18]]
);
for(let key of mapList.keys()){
  console.log(key);
}
//name age
for(let value of mapList.values()){
  console.log(value);
}
//zhangsan 18
for(let [key,value ]of mapList.entries()){
  console.log(key,value);
}
//name zhangsan
//age 18

• forEach

let mapList = new Map(
[['name','zhangsan'],
['age',18]]
);
mapList.forEach(function(value,key){
  console.log(value,key);
})
//zhangsan name
//18 "age"

需要注意的是map的key完全可以是引用類型

let mapList = new Map();
let obj = {};
mapList.set(obj,{name:'zhangsan'});
console.log(mapList.get(obj));//{name:'zhangsan'}

4 WeakMap

map的閹割版，鍵只能為引用類型，沒有size屬性，沒有clear方法，不能遍歷
ES6總篇--目錄