javascript Object 与ES6 Map 对比

Object 的键名key只可以是String 或者数字，或者Symbol,而Map的key它可以是任何类型。

一、取出Objeect 和Map 的键名Key

我们通常取出Object的键名用for in 循环，

例如：let simpleObj = {

　　　　　　　'keyOne' :  '键值一',

　　　　　　　'keyTwo' :  '键值二',

　　　　　　　'keyThree' :  '键值三'

　　　　　　　}

for (const key in simpleObj) {

            console.log(key)

        }

输出结果：keyOne、keyTwo、keyThree

··········································································································································

const m = new Map([

      ['xkey', 1],

      ['ykey', 2]

    ]);

    for (const iterator of m) {

      console.log(iterator[0])

    }

输出结果：xkey   ykey

··········································································································································

    m.forEach(element => {

      console.log(element)

    });

 输出结果：1,2

二、读取/删除元素时的区别

Obj:

//或者使用 ES2020 新增的条件属性访问表达式来读取

    o?.x; // 1

    o?.['y']; // 2

    //删除

    delete o.b;

Map:

const o = {

      x: 'centos',

      y: 'nbclass'

    };

    //读取

    o.x; // centos

    o['y']; // nbclass

    //新增/修改

    o.x = 1;

    o['y'] = 2;

    const mappp = new Map();

    //新增/修改

    mappp.set('x', 1);

    mappp.set('b', 3);

    console.log(mappp);

输出结果：{"x" => 1, "b" => 3}

    //读取

    mappp.get('x');

    console.log(mappp);

输出结果：Map(2) {"x" => 1, "b" => 3}

    //删除

    mappp.delete('b');

    console.log(mappp);

输出结果：Map(1) {"x" => 1}