Object.prototype.propertyIsEnumerable()
The propertyIsEnumerable()
method returns a Boolean
indicating whether the specified property is enumerable and is the object's own
property.
Syntax
propertyIsEnumerable(prop)
Parameters
prop
-
The name of the property to test.
Return value
A true
or false
value indicating whether the specified property is enumerable and is
the object's own property.
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
.
Examples
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
User-defined vs. built-in objects
The following example demonstrates the enumerability of user-defined vs. 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
Direct vs. 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() { 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 iterable 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
Specifications
Specification |
---|
ECMAScript Language Specification # sec-object.prototype.propertyisenumerable |
Browser compatibility
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