object

Objects have properties,

Attribute types

Data attributes and accessor attributes

Data attribute

Data attributes contain data values: Value
The characteristics of data attributes (used to describe the behavior of data attributes):

[[Configurable]]:
- Can we pass? delete Delete attributes to redefine attributes
- Can you modify attributes?Characteristic
- Can you change attributes to accessor attributes?
[[Enumerable]]
-Indicate whether it can pass for-in Loop return properties
[[Writable]]
-Can you modify attributes?value
[[Value]]
-The data value containing this property is the default read-write location of the property undefined

Modified features:
Object.defineProperty() method: -(ES5)
Object.defineProperty(obj, "name", [descriptor object})

var person = {};
Object.defineProperty(person, "name", {
    writable: false,//Characters cannot modify the value of attributes 
    value: "Nicholas"//The feature book is read-write but read-only because of writable:false

    /*descriptor object*/
});
alert(person.name); //"Nicholas"
person.name = "Greg";
alert(person.name); //"Nicholas"
/*Elevation Code Data Properties Example01.htm [p140]*/

var person = {};
Object.defineProperty(person, "name", {
configurable: false,
//- Attributes cannot be redefined by deleting attributes (1)
//- Property that *** cannot modify attributes *** (2)
//- Attributes cannot be changed to accessor attributes (3)

value: "Nicholas"
});
//Throw wrong
Object.defineProperty(person, "name", {
configurable: true,//Because (2) Correct the error report again at this time
value: "Nicholas"
});  

/*When calling the Object.defineProperty() method, if not specified, the default values for configurable, enumerable, and writable features are false*/

/*All three default values are true when setting properties directly on objects*/

Accessor properties

Accessor properties do not contain data values: (no Value)
Read: getter() function
Write: setter() function
The characteristics of accessor attributes:

Use Object.defineProperty() to define

var book = {
    _year: 2004,//Represents properties that can only be accessed through object methods
    edition: 1
};
Object.defineProperty(book, "year", {
//Year is an accessor attribute, affecting the _year and edition attributes
    get: function(){
            return this._year;//Returns the value of the _year attribute
        },
    set: function(newValue){
            if (newValue > 2004) {
            this._year = newValue;//Revaluation_year
            this.edition += newValue - 2004;//Relevance processing edition
            }
        }
});
book.year = 2005;
alert(book.edition); //2
//Elevation - Accessor Properties Example01. HTM [p141]

var book = {
    _year: 2004,
    edition: 1
};
//Old methods for defining accessors
book.__defineGetter__("year", function(){
    return this._year;
});
book.__defineSetter__("year", function(newValue){
    if (newValue > 2004) {
    this._year = newValue;
    this.edition += newValue - 2004;
    }
});
book.year = 2005;
alert(book.edition); //2
//AccessorPropertiesExample02.htm[p142]

Define multiple attributes

Object.defineProperties() method.

var book = {};
Object.defineProperties(book, {
    _year: {
    value: 2004
    },
    edition: {
    value: 1
    },
    year: {
        get: function(){
            return this._year;
        },
        set: function(newValue){
            if (newValue > 2004) {
            this._year = newValue;
            this.edition += newValue - 2004;
            }
        }
    }
});
//MultiplePropertiesExample01.htm

Features of read attributes

Object.getOwnPropertyDescriptor() method

Two parameters are included:
Objects where attributes are located
The property name of the descriptor to read.
Return value: An object.
If it is an accessor property,
Attributes are configurable, enumerable, get, and set.
If it is a data attribute,
Attributes are configurable, enumerable, writable, and value

var book = {};
Object.defineProperties(book, {//Define multiple attributes
    _year: {
        value: 2004
    },
    edition: {
        value: 1
    },
    year: {
        get: function() {
            return this._year;
        },
        set: function(newValue) {
            if(newValue > 2004) {
                this._year = newValue;
                this.edition += newValue - 2004;
            }
        }
    }
});
var descriptor = Object.getOwnPropertyDescriptor(book, "_year");//Getting descriptor objects
alert(descriptor.value); //2004
alert(descriptor.configurable); //false
alert(typeof descriptor.get); //"undefined"
var descriptor = Object.getOwnPropertyDescriptor(book, "year");
alert(descriptor.value); //undefined
alert(descriptor.enumerable); //false
alert(typeof descriptor.get); //"function"
                //GetPropertyDescriptorExample01.htm[p143-144]

Object.getOwnPropertyDescriptor() method