Object.defineProperty

发表于

Object.defineProperty

API
Object.defineProperty(obj, prop, descriptor)

  • obj:[Object] 目标对象
  • prop:[String] 需要定义或者修改的属性
  • descriptor:[Object] 配置属性 {enumerable,configurable,writable, get,set,value }

enumerable:[Boolean] default:true,true 时 forin是否可枚举
configurable：[Boolean]
value：default:undefined.
writable：[Boolean] default:true
set:[Function] default:undefined
get:[Function] default:undefined

configurable

configurable:[Boolean] ： default:true。是否能被删除或者修改

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var obj = Object.create(null)
Object.defineProperty(obj,'test',{
    value:1,
    configurable:false,
})
console.log(`delete test`)
delete obj.test //false
console.log(`test`,obj.test) //1
console.log(`set test data 2`)
obj.test = 2
console.log(`modify test value`,obj.test) //1

enumerable

enumerable:[Boolean] ： default:true。是否能被枚举 forin,Object.keys

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var obj = Object.create(null)
Object.defineProperty(obj,'test',{
    value:1,
    enumerable:false,
})
console.log(`Object.keys`,Object.keys(obj))
console.log(`-----forin start----`)
for(let p in obj){
    console.log(p)
}
console.log(`-----forin end----`)

writable

为false时不能被重写

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var obj = Object.create(null)
Object.defineProperty(obj,'test',{
    value:1,
    writable:false,
})
obj.test = 2
console.log(`set value 2 ,get value`,obj.test) //set value 2 ,get value 1

get/set

当使用了get/set方法，不允许使用writable和value这两个属性

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var obj = Object.create(null)
var value
Object.defineProperty(obj,'test',{
    configurable: true,
    enumerable: true,
    get(){
        console.log('get val',value)
        return value
    },
    set(newVal){
        console.log('set newVal',newVal)
        value = newVal
    }
})
obj.test = 1 //set newVal 1
obj.test //get val 1