Core JavaScript 1.5 Reference:Global Objects:Object:propertyIsEnumerable

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Contents 1 Summary 2 Syntax 3 Parameters 4 Description 5 Examples 5.1 Example: A basic use of propertyIsEnumerable 5.2 Example: User-defined versus built-in objects 5.3 Example: Direct versus inherited properties 6 See also

[edit] Summary

Returns a boolean indicating whether the specified property is enumerable.

[edit] Syntax

obj.propertyIsEnumerable(prop);

[edit] Parameters

prop 

The name of the property to test.

[edit] Description

Every object has a propertyIsEnumerable method. This method can determine whether the specified property in an object can be enumerated by a for...in loop, with the exception of properties inherited through the prototype chain. If the object does not have the specified property, this method returns false.

[edit] Examples

[edit] Example: A basic use of propertyIsEnumerable

The following example shows the use of propertyIsEnumerable on objects and arrays:

var o = {};
var a = [];
o.prop = 'is enumerable';
a[0] = 'is enumerable';

o.propertyIsEnumerable('prop');   // returns true
a.propertyIsEnumerable(0);        // returns true

[edit] Example: User-defined versus built-in objects

The following example demonstrates the enumerability of user-defined versus built-in properties:

var a = ['is enumerable'];

a.propertyIsEnumerable(0);          // returns true
a.propertyIsEnumerable('length');   // returns false

Math.propertyIsEnumerable('random');   // returns false
this.propertyIsEnumerable('Math');     // returns false

[edit] Example: Direct versus inherited properties

var a = [];
a.propertyIsEnumerable('constructor');         // returns false

function firstConstructor()
{
  this.property = 'is not enumerable';
}

function secondConstructor()
{
  this.method = function method() { return 'is enumerable'; };
}

secondConstructor.prototype = new firstConstructor;

var o = new secondConstructor();
o.arbitraryProperty = 'is enumerable';

o.propertyIsEnumerable('arbitraryProperty');   // returns true
o.propertyIsEnumerable('method');              // returns true
o.propertyIsEnumerable('property');            // returns false

o.property = 'is enumerable';

o.propertyIsEnumerable('property');            // returns true

[edit] See also

for...in