JS 对象基本用法

内容1：声明对象的两种语法

• 简单语法：

let obj = {name:'xiaoli'}

• 标准语法：

let obj2 = new Object({name:'xiaohong'})

内容2：如何删除对象的属性

• delete方法：

delete obj2.name
delete ob2['name']

delete obj3[age] //age is not defined

let age = 'age'
delete obj3[age] //true

内容3：如何查看对象的属性

• Object.keys()，查看所有的键
• Object.values()，查看所有的值
• Object.entries()，查看所有的键和值
• console.dir(obj3),查看自身和共有属性

> let obj3 = {name:'lili',age:19,gender:'woman'}
<· undefined

> obj3
<· {name: "lili", age: 19, gender: "woman"}

> Object.keys(obj3)
<· (3) ["name", "age", "gender"]

> Object.values(obj3)
<· (3) ["lili", 19, "woman"]

> Object.entries(obj3)
<· 
0: (2) ["name", "lili"]
1: (2) ["age", 19]
2: (2) ["gender", "woman"]
length: 3

> console.dir(obj3)
Object
age: 19
gender: "woman"
name: "lili"
__proto__: Object
<· undefined

内容4：如何修改或增加对象的属性

• 点方法：obj3.age = 21
• 中括号方法：obj3['name'] = 'liuli'

obj3.age = 21

obj3['name'] = 'liuli'

obj3[gender] = 'not a man' //gender is not defined

let gender = 'gender'
obj3[gender] = 'no a man'

内容5：'name' in obj和obj.hasOwnProperty('name') 的区别

• 'name' in obj，只能查看属性是否存在，不能判断该属性是否属于自己还是共有
• obj.hasOwnProperty('toString')，可以判断一个属性是自身还是共有

> 'name' in obj3
<· true

> obj3.hasOwnProperty('name')
<· true

> obj3.toString()
<· "[object Object]"

> obj3.hasOwnProperty('toString')
<· false