JavaScript: The Definitive Guide, 6th Edition

Name

Object.getOwnPropertyDescriptor() — query property attributes

Availability

ECMAScript 5

Synopsis

Object.getOwnPropertyDescriptor(o, name)

Arguments

o

The object that is to have its property attributes queried.

name

The name of the property (or index of the array element) to query.

Returns

A property descriptor object for the specified property of the specified object, or undefined if no such property exists.

Description

Object.getOwnPropertyDescriptor() returns a property descriptor for the specified property of the specified object. A property descriptor is an object that describes the attributes and value of a property. See the sub-section below for complete details. Note that this is not a method to be invoked on an object: it is a global function and you must pass an object to it.

Property Descriptors

A property descriptor is an ordinary JavaScript object that describes the attributes (and sometimes the value) of a property. There are two kinds of JavaScript properties. A data property has a value and three attributes: enumerable, writable, and configurable. An accessor property has a getter and/or a setter method as well as enumerable and configurable attributes.

The descriptor for a data property looks like this:

{
    value:        /* any JavaScript value */,
    writable:     /* true or false */,
    enumerable:   /* true or false */,
    configurable: /* true or false */
}

The descriptor for an accessor property looks like this:

{
    get:          /* function or undefined: replaces the property value */,
    set:          /* function or ...