defineProperties

Summary

Adds one or more properties to an object, and/or modifies attributes of existing properties.

Syntax

object.defineProperties( object , descriptors )

object: Required. The object on which to add or modify the properties. This can be a native JavaScript object or a DOM object.
descriptors: Required. A JavaScript object that contains one or more descriptor objects. Each descriptor object describes a data property or an accessor property.

Return Value

The object that was passed to the function.

Examples

Adding Properties

In the following example, the Object.defineProperties function adds a data property and an accessor property to a user-defined object.

The example uses an object literal to create the descriptors object with the newDataProperty and newAccessorProperty descriptor objects.

var newLine = "<br />";

var obj = {};
Object.defineProperties(obj, {
    newDataProperty: {
        value: 101,
        writable: true,
        enumerable: true,
        configurable: true
    },
    newAccessorProperty: {
        set: function (x) {
            document.write("in property set accessor" + newLine);
            this.newaccpropvalue = x;
        },
        get: function () {
            document.write("in property get accessor" + newLine);
            return this.newaccpropvalue;
        },
        enumerable: true,
        configurable: true
    });

// Set the accessor property value.
obj.newAccessorProperty = 10;
document.write ("newAccessorProperty value: " + obj.newAccessorProperty + newLine);

// Output:
// in property set accessor
// in property get accessor
// newAccessorProperty value: 10

Like the previous example, the following example adds properties dynamically instead of with an object literal.

var newLine = "<br />";

// Create the descriptors object.
var descriptors = new Object();

// Add a data property descriptor to the descriptors object.
descriptors.newDataProperty = new Object();
descriptors.newDataProperty.value = 101;
descriptors.newDataProperty.writable = true;
descriptors.newDataProperty.enumerable = true;
descriptors.newDataProperty.configurable = true;

// Add an accessor property descriptor to the descriptors object.
descriptors.newAccessorProperty = new Object();
descriptors.newAccessorProperty.set = function (x) {
    document.write("in property set accessor" + newLine);
    this.newaccpropvalue = x;
};
descriptors.newAccessorProperty.get = function () {
    document.write("in property get accessor" + newLine);
    return this.newaccpropvalue;
};
descriptors.newAccessorProperty.enumerable = true;
descriptors.newAccessorProperty.configurable = true;

// Call the Object.defineProperties function.
var obj = new Object();
Object.defineProperties(obj, descriptors);

// Set the accessor property value.
obj.newAccessorProperty = 10;
document.write ("newAccessorProperty value: " + obj.newAccessorProperty + newLine);

// Output:
// in property set accessor
// in property get accessor
// newAccessorProperty value: 10

Modifying Properties

To modify property attributes for the object, add the following code. The Object.defineProperties function modifies the writable attribute of newDataProperty , and modifies the enumerable attribute of newAccessorProperty. It adds anotherDataProperty to the object because that property name does not already exist.

Object.defineProperties(obj, {
        newDataProperty: { writable: false },
        newAccessorProperty: { enumerable: false },
        anotherDataProperty: { value: "abc" }
    });

Remarks

The descriptors argument is an object that contains one or more descriptor objects.

A data property is a property that can store and retrieve a value. A data property descriptor contains a value attribute, a writable attribute, or both. For more information, see Data Properties and Accessor Properties.

An accessor property calls a user-provided function every time the property value is set or retrieved. An accessor property descriptor contains a set attribute, a get attribute, or both.

If the object already has a property that has the specified name, the property attributes are modified. For more information, see Object.defineProperty Function.

To create an object and add properties to the new object, you can use the Object.create Function.

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