August 2006
Intermediate to advanced
1018 pages
34h 13m
English
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Name
Object.propertyIsEnumerable( ): will property be seen by a for/in loop? — ECMAScript v3
Synopsis
object.propertyIsEnumerable(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 and if
that property is enumerable, which means that it would be enumerated by a
for/in loop on
object.
Description
The for/in statement loops
through the enumerable properties of an object. Not all properties
of an object are enumerable, however: properties added to an object
by JavaScript code are enumerable, but the predefined properties
(such as methods) of built-in objects are not usually enumerable.
The propertyIsEnumerable( )
method provides a way to distinguish between enumerable and
nonenumerable properties. Note, however, that the ECMAScript
specification states that propertyIsEnumerable( ) does not examine
the prototype chain, which means it works only for local properties
of an object and does not provide any way to test the enumerability
of inherited properties.
Example
var o = new Object( ); // Create an object
o.x = 3.14; // Define a property
o.propertyIsEnumerable("x"); // true: property x is local and enumerable
o.propertyIsEnumerable("y"); // false: o doesn't have a property y
o.propertyIsEnumerable("toString"); // false: toString property is inherited
Object.prototype.propertyIsEnumerable("toString"); // false: nonenumerableSee Also
Function.prototype, Object.hasOwnProperty( ...
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