Three properties of javascript objects

Object characteristics:

1. writable: writable

writable indicates whether the value of the property can be set

let obj = {age:10}
obj.age = 1 // Reassign the property console.log(obj.age) //1

2. enumerable: enumerable

The enumerable attribute refers to whether the property name can be returned in for/in loop. By default, both owned and inherited properties can be enumerated.

let obj = {name:"zhang", age:20, sex:"male"}

let newObj = Object.create(obj)
newObj.height = 200

for(p in newObj){
    console.log(p,"->", newObj[p])
}

Output:

height -> 200
name -> zhang
age -> 20
sex -> male

3. Configurable: Configurable

configurable indicates whether the attribute can be deleted through delete

let obj = {name:"jim"}

delete obj.name // After deletion, the property will no longer exist console.log(obj.name) //undefined

The above three properties of the object's own attributes are true by default. If you want to modify the default values ​​of these characteristics, you can use Object.defineProperty() method. defineProperty receives three parameters: object, property name to be modified, and feature value object.

For example, if you want to set the writable property of the sex property to false, you can use the defineProperty() method to do this.

let obj = {name:"zhang", age:20, sex:"male"}
Object.defineProperty(obj, "sex", {writable:false})
obj.sex = "female"
console.log(obj.sex) // Male

After setting writable to false , even if the sex attribute is reassigned to female, its value is still male. Similar operations can be used to configure the enumerable and configurable characteristics of attributes.

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