es6的Map()構造函數

普通的object對象是鍵值對的集合，但對于它的鍵卻有著嚴苛的要求，必須是字符串，這給我們平時帶來很多的不方便

Map函數類似于對象，但它是一個更加完美的簡直對集合，鍵可以是任意類型

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• set()方法可以向map實例對象中添加一組鍵值對

let a=new Map();
let key={name:"ww",sex:"man"};
a.set(key,'ABC');
console.log(a)//{{name:"ww",sex:"man"}=>"ABC"}

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

• get()方法可以向map對象獲取一個屬性值

let a=new Map();
let key={name:"ww",sex:"man"};
a.set(key,'ABC');
console.log(a.get(key))//'ABC'

• has()方法檢測map對象中是否存在某個屬性，返回bool
• delete()方法刪除map對象中某個鍵，返回bool

let a=new Map();
let key={name:"ww",sex:"man"};
a.set(key,'ABC');
console.log(a.has(key))//true
a.delete(key);
console.log(a.has(key))//false

• ?Map()函數接受數組作為參數，最少必須是二維雙數組，長度為2

let a=new Map([['name','wangwei'],['sex','man']]);
console.log(a)//{'name'=>'wangwei','sex'=>'man'}

let b=new Set([['a','A'],['b','B']]);
let c=new Map(b);
console.log(c)//{'a'=>'A','b'=>'B'}

• Map()函數接受iterator接口，Map可以自己賦值，注意：不可以對象初始化Map

let b=new Set([['a','A'],['b','B']]);
let c=new Map(b);
let d=new Map(c);
console.log(d)

• Map函數初始化，注意：數組引用必須相同才會覆蓋

let a=['a','A'];
let b=['a','A'];
let c=new Map();
c.set(a,1);
c.set(b,2);
console.log(c.get(a),c.get(b))// 1 2

let a=['a','A'];
let b=a;
let c=new Map();
c.set(a,1);
c.set(b,2);
console.log(c.get(a),c.get(b))// 2 2

• size屬性獲取map對象成員個數
• clear()屬性清除map對象的成員
• forEach()遍歷
• keys()
• entries()
• values()

let a=new Map([[1,'a'],[2,'b'],[3,'c']]);
for(let i of a){console.log(i)
}
//[1,'a'],[2,'b'],[3,'c']
for(let i of a.keys()){console.log(i)
}//1 2 3
for(let i of a.values()){console.log(i)
}//a b c
for(let [key,value] of a.entries()){console.log(key,value)
}//1 'a'  2  'b'   3  'c'

• Map轉換為數組 方法 ...|...keys()|...values|...entries

let a=new Map([[1,'a'],[2,'b'],[3,'c']]);
let b=[...a];
console.log(b)//[[1,'a'],[2,'b'],[3,'c']]
let c=[...a.keys()];
console.log(c)//[1,2,3]
let d=[...a.values()];
console.log(d);//["a", "b", "c"]
let e=[...a.entries()];
console.log(e);//[[1,'a'],[2,'b'],[3,'c']]

• ?Map對象轉換為對象，注意：Map的鍵必須全部是字符串

let a=new Map([['a','A'],['b','B'],['c','C']]);
let b={};
for(let [key,value] of a){b[key]=value
}
console.log(b)//{a: "A", b: "B", c: "C"}

• 對象轉換為Map

let a=new Map();
let b={a: "A", b: "B", c: "C"};
for(let i in b){a.set(i,b[i])
}
console.log(a)//{"a" => "A", "b" => "B", "c" => "C"}

• JSON轉對象，可以先轉換為數組或者對象再轉換為map
• weakMap()鍵必須是對象