js Object的属性 Configurable,Enumerable,Writable,Value,Getter,Setter

对象的数据属性

Configurable,Enumerable,Writable,Value

var person = {}
Object.defineProperty(person,'name',{
    configurable:false,//能否使用delete、能否需改属性特性、或能否修改访问器属性、，false为不可重新定义，默认值为true
    enumerable:false,//对象属性是否可通过for-in循环，flase为不可循环，默认值为true
    writable:false,//对象属性是否可修改,flase为不可修改，默认值为true
    value:'xiaoming' //对象属性的默认值，默认值为undefined
});

//value
console.log(person);//xiaoming，默认value

//writable
person.name="qiang";
console.log(person);//xiaoming，不可修改value

//enumerable
for(var i in person){
    console.log(person[i]) //无结果，不可循环
}

//configurable
delete person.name
console.log(person.name)//xiaoming，不可删除

Object.defineProperty(person,'name',{
    configurable:true //不可修改，将抛出错误
});

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访问器属性

getter，setter

var book = {
    _year: 2004,//属性前面加_，代表属性只能通过对象方法访问
    edition: 0
}
Object.defineProperty(book,'year',{
    get: function(){
        return this._year;
    },
    set: function(newValue){
        if(newValue > 2004){
            this._year = newValue;
            this.edition += newValue - 2004
        }
    }
});
console.log(book.year)//2004
book.year = 2006;
console.log(book.year)//2006
console.log(book.edition)//2

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定义多个属性

Object.defineProperties

var book = {};
   Object.defineProperties(book, {
       _year: {
        value:2004,
        writable:true
       },
       edition: {
           value: 0,
           writable:true
       },
       year: {
           get: function() {
               return this._year;
           },
           set: function(newValue) {
               if (newValue > 2004) {
                   this._year = newValue;
                   this.edition += newValue - 2004
               }
           }
       }
   });
   console.log(book.year) //2004
   book.year = 2006;
   console.log(book.year) //2006
   console.log(book.edition) //2

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读取属性

var book = {};
    Object.defineProperties(book, {
        _year: {
            value:2004,
            writable:true
        },
        edition: {
            value: 0,
            writable:true
        },
        year: {
            get: function() {
                return this._year;
            },
            set: function(newValue) {
                if (newValue > 2004) {
                    this._year = newValue;
                    this.edition += newValue - 2004
                }
            }
        }
    });
    console.log(book.year) //2004
    book.year = 2006;
    console.log(book.year) //2006
    console.log(book.edition) //2
    //读取属性
    var descriptor__year = Object.getOwnPropertyDescriptor(book,'_year');
    var descriptor_year = Object.getOwnPropertyDescriptor(book,'year');

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console.log(descriptor__year ) 

console.log(descriptor_year ) 

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