JavaScript中Map和Object的区别详解

const smbObj = {
  1: 'ShowMeBug',
  2: 'ShowMeMoney'  
};

const smbMap = new Map([
  [1, 'ShowMeBug'],
  [2, 'ShowMeMoney']
]);

//因为键已经被转换成字符串，所以无论是获取数字1还是字符串'1'的值时，得到的结果都一样
console.log(smbObj[1]);
//'ShowMeBug'
console.log(smbObj['1']);
//'ShowMeBug'

//Map 的键可以为任意类型，数字 1 的键和字符串 '1' 的键并不一样
console.log(smbMap[1]);
//'ShowMeBug'
console.log(smbMap['1']);
//undefined

//打印 Object.prototype，
//你会发现它还有 
//hasOwnProperty、
//isPrototypeOf、
//toLocaleString、
//toString 等属性
console.log(Object.prototype);

const socalledEmptyObject = {};
console.log(socalledEmptyObject['toString']);
//ƒ toString() { [native code] }

//Object.create(null) 能构建出没有原型的对象
const emptyObject = Object.create(null);
console.log(emptyObject['toString']);
//undefined

const smbObj = {
  2: 'ShowMeMoney',
  1: 'ShowMeBug'  
};

const keys = Object.keys(smbObj);
console.log(keys);
//["1", "2"]

const keyValuePairs = Object.entries(smbObj);
console.log(keyValuePairs);
//["1", "ShowMeBug"]
//["2", "ShowMeMoney"]

const smbMap = new Map([
  [2, 'ShowMeMoney'],
  [1, 'ShowMeBug']
]);

const keys = smbMap.keys();
console.log(keys);
//MapIterator {2, 1}

const keyValuePairs = smbMap.entries();
console.log(keyValuePairs);
//MapIterator {2 => "ShowMeMoney", 1 => "ShowMeBug"}

smbObj[1];
//'ShowMeBug'

smbMap.get(1);
//'ShowMeBug'

smbObj.hasOwnProperty(1);
//true
smbObj.hasOwnProperty(3);
//false

smbMap.has(1);
//true
smbMap.get(3);
//false

smbObj[3] = 'ShowMeFeature';
//{ 1: 'ShowMeBug', 2: 'ShowMeMoney', 3: 'ShowMeFeature'};

smbMap.set(3, 'ShowMeFeature'); 
//{1=>'ShowMeBug', 2=>'ShowMeMoney', 3=>'ShowMeFeature'}

delete smbObj[1];

smbMap.delete(1);

const size = Object.keys(smbObj).length;
console.log(size);

console.log(smbMap.size);

const smbMap = new Map([
  [1, 'ShowMeBug'],
  [2, 'ShowMeMoney']
]);

smbMap.forEach((value, key)=>{
   console.log(`${key} - ${value}`)
});
//1 - ShowMeBug
//2 - ShowMeMoney

//Object.entries() 会以 [key, value] 键值对数组的形式返回对象的所有属性。一旦拿到这一数组，就能用 forEach 这样的数组方法了
        const smbObj = {
            1: 'ShowMeBug',
            2: 'ShowMeMoney'
        };

        Object
            .entries(smbObj)
            .forEach(([key, value]) => {
                console.log(`${key} - ${value}`)
            });
   
        //这里的key,value都是字符串，只是控制台显示时去掉了双引号
        //1 - ShowMeBug
        //2 - ShowMeMoney

const smbObj = {
  1: 'ShowMeBug',
  2: 'ShowMeMoney'  
};

const json = JSON.stringify(smbObj);
console.log(json);
//{"1":"ShowMeBug","2":"ShowMeMoney"}

const smbMap = new Map([
  [1, 'ShowMeBug'],
  [2, 'ShowMeMoney']
]);

const json = JSON.stringify(smbMap);
console.log(json);
//{}