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The propertyIsEnumerable() method returns a Boolean indicating whether the specified property is enumerable.




The name of the property to test.


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.


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

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

Example: Direct versus inherited properties

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

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

firstConstructor.prototype.firstMethod = function() {};

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

secondConstructor.prototype = new firstConstructor;
secondConstructor.prototype.constructor = secondConstructor;

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

// These return false as they are on the prototype which 
// propertyIsEnumerable does not consider (even though the last two
// are iteratable with for-in)
o.propertyIsEnumerable('prototype');   // returns false (as of JS 1.8.1/FF3.6)
o.propertyIsEnumerable('constructor'); // returns false
o.propertyIsEnumerable('firstMethod'); // returns false


Specification Status Comment
ECMAScript 3rd Edition. Standard Initial definition.
ECMAScript 5.1 (ECMA-262)
Die Definition von 'Object.prototype.propertyIsEnumerable' in dieser Spezifikation.
ECMAScript 6 (ECMA-262)
Die Definition von 'Object.prototype.propertyIsEnumerable' in dieser Spezifikation.
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Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support (Ja) (Ja) (Ja) (Ja) (Ja)
Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support (Ja) (Ja) (Ja) (Ja) (Ja) (Ja)

Gecko-specific notes

Starting in JavaScript 1.8.1 (in Firefox 3.6), propertyIsEnumerable('prototype') returns false instead of true; this makes the result compliant with ECMAScript 5.

See also

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