es6的Map()构造函数

普通的object对象是键值对的集合，但对于它的键却有着严苛的要求，必须是字符串，这给我们平时带来很多的不方便

Map函数类似于对象，但它是一个更加完美的简直对集合，键可以是任意类型

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• set()方法可以向map实例对象中添加一组键值对

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对象获取一个属性值

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

• has()方法检测map对象中是否存在某个属性，返回bool
• delete()方法删除map对象中某个键，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()函数接受数组作为参数，最少必须是二维双数组，长度为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()函数接受iterator接口，Map可以自己赋值，注意：不可以对象初始化Map

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

• Map函数初始化，注意：数组引用必须相同才会覆盖

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属性获取map对象成员个数
• clear()属性清除map对象的成员
• forEach()遍历
• 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转换为数组 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对象转换为对象，注意：Map的键必须全部是字符串

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"}

• 对象转换为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转对象，可以先转换为数组或者对象再转换为map
• weakMap()键必须是对象