6. Object扩展

1. 对象属性方法同名简写

ES6允许在括号里直接写入变量和函数，作为对象的属性和方法(说白了就是同名简写)

var id = 1007
var obj = {
  id,
  fn(){ ... }
}

等价于
var obj = {
  id: id,
  fn: function(){ ... }
}

简写应用场景

// net.js 配置调用接口并导出
function getUser(user) {
  //...
}

function setProfile(name, id) {
  //...
}
// 导出
export {
  getUser,
  setProfile
}
// 相当于
export {
  getUser:getUser,
  setProfile:setProfile
}

2. super 关键字

super指向当前对象的原型，相当于this.__proto__，且只能在对象方法中使用

var objProto = { name: 'objProto ' }
var obj = { 
  name: 'obj',
  fn(){ alert(super.name) }
}
Object.setPrototypeOf(obj,objProto)
obj.fn() // 'objProto'

注意：一些浏览器不能识别super关键字，需要babel转译

3. ...操作符解构属性

let a = {id: 107, name: 'jack'}
let b = {...a}  // {id: 107, name: 'jack'}

let c = {id: 33, age: 18}
let d = {id: 55,name:'tom'}
let e = {...c,...d} // {id:55,age:18,name:'tom'} 合并c和d，后边覆盖前边的同名属性

let f = {...[1,2,3]} // {0: 1, 1: 2, 2: 3}

4. assign

用于对象合并，将源对象的所有可枚举属性复制到目标对象Object.assign(target, obj1, ... ,obj)

let target = {a:1}
let obj1 = {b:1}
let obj2 = {c:1}

Object.assign(target,obj1,obj2)
target // {a:1,b:1,c:1}

// 等价于
target = {...target,...obj1,...obj2}

5. keys

返回由可枚举属性名组成的数组Object.keys(obj)

Object.keys({id:1007,name:'jack'}) // ['id','name']

let obj = {
  id:107,
  name:'jack'
}
Object.keys(obj).forEach(prop=>{
  alert(prop)
})

6. values、entries、fromEntries

下面是汇总：

Object.keys({key1:val1,...,key:val}) => [key1,...,key]
Object.values({key1:val1,...,key:val}) => [val1,...,val]
Object.entries({key1:val1,...,key:val}) => [[key1,val1],...,[key,val]]
Object.fromEntries([[key1,val1],...,[key,val]]) => {key1:val1,...,key:val}

用法：

// keys, values, entries
let {keys, values, entries} = Object // 还记得解构吗？
let obj = { a: 1, b: 2, c: 3 }

for (let key of keys(obj)) {
  console.log(key) // 'a', 'b', 'c'
}

for (let value of values(obj)) {
  console.log(value) // 1, 2, 3
}

for (let [key, value] of entries(obj)) {
  console.log([key, value]) // ['a', 1], ['b', 2], ['c', 3]
}

// fromEntries
Object.fromEntries([
  ['id', 107],
  ['age', 18]
])
// { id: 107, age: 18}

// 应用
const map = new Map().set('foo', true).set('bar', false);
Object.fromEntries(map)
// { foo: true, bar: false }