Mozilla Developer Network
Summary
Returns a Boolean indicating whether the specified property is enumerable.
Method of Object |
|
|---|---|
| Implemented in | JavaScript ? |
| ECMAScript Edition | ECMAScript 3rd Edition |
Syntax
obj.propertyIsEnumerable(prop)Parameters
-
prop - The name of the property to test.
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.
Note: 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.Examples
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