ES6对象扩展

Posted 2021-09-07 飞鹰

今天小编和大家一块聊聊ES6中对对象的扩展语法，还有一些常用的语法，相信在不久的将来，肯定会在Vue中看到对象的影子。大家还可以关注我的微信公众号，蜗牛全栈。
一、属性的简洁表示法：主要针对值用变量表示，并且键和值的变量一致
1、普通对象声明

let obj = {
    name:"lilei",
    age:34
}
console.log(obj)

2、简洁表示法

let name = "lilei"
let age = 34
let obj = {
    name,
    age
}

3、属性名表达式：主要针对键为变量的情况，需要将变量加上方括号即可

let s = "school"
let obj = {
    name:"lilei",
    age:34,
    s:"school"
}
console.log(obj) // {name:"lilei",age:34,s:"school"}
let s = "school"
let obj = {
    name:"lilei",
    age:34,
    [s]:"school"
}
console.log(obj) // {name:"lilei",age:34,school:"school"}

4、对象内的函数

let s = "school"
let obj = {
    name:"lilei",
    age:34,
    [s]:"school",
    study:function(){
        console.log(this.name+"正在学习")
    }
}
obj.study() // lilei正在学习
let s = "school"
let obj = {
    name:"lilei",
    age:34,
    [s]:"school",
    study:() => {
        console.log(this.name+"正在学习")
    }
}
obj.study() // 报错：can\'t read property \'name\' of undefind(原因就是箭头函数的this指向问题，参见小编的箭头函数文章)
let s = "school"
let obj = {
    name:"lilei",
    age:34,
    [s]:"school",
    study(){
        console.log(this.name+"正在学习")
    }
}
obj.study() // lilei正在学习

二、Object.is()：相当于严格判断的三个等号

console.log(Object.is(2,\'2\')) // false
console.log(Object.is(NaN,NaN)) // true
console.log(Object.is(+0,-0)) // false
let obj1 = {
    name:"lilei",
    age:34
}
let obj2 = {
    name:"lilei",
    age:34
}
console.log(obj1 == obj2) // false 
console.log(Object.is(obj1,obj2)) // false 引用类型的堆内存地址不一致
let obj1 = {
    name:"lilei",
    age:34
}
let obj2 = obj1
console.log(Object.is(obj1,obj2)) // true 引用类型的堆内存地址一致

三、扩展运算符与Object.assign()

let x = {
    a:3,
    b:4
}
let y = {...x}
console.log(y) // {a:3,b:4}
let x = {
    a:3,
    b:4
}
let y = {}
Object.assign(y,x)
console.log(y) // {a:3,b:4}
let x = {
    a:3,
    b:4
}
let y = {
    c:5,
    a:6
}
Object.assign(y,x)
console.log(y) // {a:6,b:4,c:5}

四、in：判断数组指定下标是否存在值；判断对象是否存在指定键

let x = {
    a:3,
    b:4
}
console.log("a" in x) // true
let arr = [1,2,3]
console.log(3 in arr) // false 判断下表为3的位置是否有值，而不是值3

五、对象的遍历
方法1

let obj = {
    name:"lilei",
    age:34,
    school:"School"
}
for(let key in obj){
    console.log(key,obj[key])
}

方法2

let obj = {
    name:"lilei",
    age:34,
    school:"School"
}
Object.keys(obj).forEach(key => {
    console.log(key,obj[key])
})

方法3

let obj = {
    name:"lilei",
    age:34,
}
Object.getOwnPropertyNames(obj).forEach(key => {
    console.log(key,obj[key])
})

方法4

let obj = {
    name:"lilei",
    age:34,
    school:"School"
}
Reflect.ownKeys(obj).forEach(key => {
    console.log(key,obj[key])
})