JavaScript Object Properties

JavaScript Object Properties

In addition to including names and values, attributes contain some of their writable, enumerable, configurable features. There are two types of properties in JavaScript: Data properties and accessor properties.

Data properties:

Configurable: Indicates whether the property can be redefined by deleting the property through the delete, modifying the property's attributes, or changing the property to an accessor property.

Enumerable: Indicates whether the property can be returned through the for-in loop.

Writable: Indicates whether the value of the property can be modified.

Value: The data value that contains this property.

To modify the properties default attribute, use Object.defineproperty ().

        var person = {};        Object.defineproperty (person, "name", {            configurable:false,//) Once the attribute is defined as not configurable, it can no longer be modified to be configurable.            Writable:false,            value: "Nicholas"        });        Delete Person.name;        alert (person.name); Nicholas        person.name = "Michael";        alert (person.name); Nicholas

Accessor properties:

Configurable: Indicates whether the property can be redefined by deleting the property through the delete, modifying the property's attributes, or changing the property to an accessor property.

Enumerable: Indicates whether the property can be returned through the for-in loop.

Get: The function that is called when the property is read.

Value: The function that is called when the property is written.

       var book = {            _year:2004,            edition:1        };                  Object.defineproperty (book, "Year", {            get:function () {                return this._year;            },            set:function (newvalue {                            if (NewValue > 2004) {                    this._year = newvalue;                    This.edition + = newValue-2004;}}        );                Book.year = 2005;        alert (book.edition);   2
        Note:this example only works in browsers that has implemented the ECMAScript 5

Define multiple properties Object.defineproperties ()

         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;}}}                );                   Book.year = 2005;        alert (book.edition);   2
        Note:this example only works in browsers that has implemented the ECMAScript 5

Properties of the Read attribute

        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;        }                }            }        });        var descriptor = object.getownpropertydescriptor (book, "_year");          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"
Note:this example only works in browsers that has implemented the ECMAScript 5
        

JavaScript Object Properties