JavaScript: The Definitive Guide, Fourth Edition

Name

Object.hasOwnProperty( ) — check whether a property is inherited

Availability

JavaScript 1.5; JScript 5.5; ECMAScript v3

Synopsis

                  object.hasOwnProperty(propname)

Arguments

propname

A string that contains the name of a property of object.

Returns

true if object has a noninherited property with the name specified by propname. Returns false if object does not have a property with the specified name or if it inherits that property from its prototype object.

Description

As explained in Chapter 8, JavaScript objects may have properties of their own, and they may also inherit properties from their prototype object. The hasOwnProperty( ) method provides a way to distinguish between inherited properties and noninherited local properties.

Example

var o = new Object(  );          // Create an object
o.x = 3.14;                      // Define a noninherited local property
o.hasOwnProperty("x");           // Returns true: x is a local property of o
o.hasOwnProperty("y");           // Returns false: o doesn't have a property y
o.hasOwnProperty("toString");    // Returns false: toString property is inherited

See Also

Function.prototype, Object.propertyIsEnumerable( ); Chapter 8