ES6:对象扩展

1.属性的简洁表达法

var foo = '123'
//ES5
var obj = {
    foo : foo,
    getMsg : function (){
        console.log(this.foo,this.name,this.age)
    }
}
//ES6
var obj = {
    foo,
    getMsg (){
        console.log(this.foo,this.name,this.age)
    }
}

2.属性名表达式

//ES5
var obj= {}
obj.name = 'kiwi';
obj['a' + 'ge'] = 27;
//ES6
var name = 'name';
var age = 'age';
var obj = {
    [name] : 'kiwi',
    [age] : 27
}

3.属性的可枚举性

var obj = {
    name : 'kiwi',
    age : 27
}
console.log(Object.getOwnPropertyDescriptor(obj, 'name'))
//enumerable : true
console.log(Object.getOwnPropertyDescriptor(Object.prototype, 'toString'))
//enumerable : false

4.新的API

Object.is()

Object.is()和 === 绝大多数是一样的，是 === 的升级版。

console.log(Object.is('foo','foo'))//true

console.log(Object.is(NaN,NaN))//true
console.log(NaN === NaN);//false

console.log(Object.is(+0, -0))//false
console.log(+0 === -0);//true

Object.assign()

Object.assign() 用来将多个原对象的可枚举属性复制到目标对象当中。

var obj = {}
var obj1 = {name : 'kiwi'}
var obj2 = {age : 27}
var newObj = Object.assign(obj, obj1, obj2);
//obj -> {name : 'kiwi', age : 27}
//newObj -> {name : 'kiwi', age : 27}

隐式转换,将数据值转为对象后再赋值（null undefined不行）

var newObj1 = Object.assign(2);
//number{2}
var newObj2 = Object.assign('123');
//string{"123"}

应用：添加方法和属性

var obj = {}
var obj1 = {name : 'kiwi', age : 27}
var obj2 = {getName(){console.log('jch')}}
var newObj = Object.assign(obj,obj1,obj2);
console.log(newObj)
//{name: "kiwi", age: 27, getName: ƒ}

Object.keys()、Object.values()、Object.entries()

都是返回数组，且成员是参数对象自身的（不含继承的）所有可遍历（enumerable）属性。Object.keys()是键名，Object.values()是键值Object.entries()是键值对数组

var obj = [2, 4, 6]
var keys = Object.keys(Obj)
//["0", "1", "2"]
var values = Object.values(Obj)
//[2, 4, 6] chrom不支持
var entries = Object.entries(Obj)
//["0":2, "1":4, "2":6]

Object.entries()应用：1）遍历对象的属性

let obj = { sasa : 'fish', kiwi : 'dog' };  
for (let [key, value] of Object.entries(obj)) {  
  console.log(  
  `My name is ${key},I like ${value} .`
  );  
}
//My name is sasa,I like fish 
a.html:31 My name is kiwi,I like dog

Object.entries()应用：2）将对象转为真正的 Map 结构

const obj = { name: 'kiwi', age: 27 };  
const map = new Map(Object.entries(obj));  
console.log(map );
// Map{"name" => "kiwi", "age" => 27}