The hasOwnProperty()
method returns a boolean indicating whether the object has the specified property as its own property (as opposed to inheriting it).
Syntax
obj.hasOwnProperty(prop)
Parameters
Return value
A Boolean
indicating whether or not the object has the specified property as own property.
Description
All descendents of Object
inherit the hasOwnProperty
method. This method can be used to determine whether an object has the specified property as a direct property of that object; unlike the in
operator, this method does not check for a property in the object's prototype chain. If an Object
is an Array
, hasOwnProperty
method can check whether an index exists.
Note
hasOwnProperty
returns true even if the value of the property is null
or undefined
.
o = new Object(); o.propOne = null; o.hasOwnProperty('propOne'); // returns true o.propTwo = undefined; o.hasOwnProperty('propTwo'); // returns true
Examples
Using hasOwnProperty to test for a property's existence
The following example determines whether the o
object contains a property named prop
:
o = new Object(); o.hasOwnProperty('prop'); // returns false o.prop = 'exists'; o.hasOwnProperty('prop'); // returns true
Direct vs. inherited properties
The following example differentiates between direct properties and properties inherited through the prototype chain:
o = new Object(); o.prop = 'exists'; o.hasOwnProperty('prop'); // returns true o.hasOwnProperty('toString'); // returns false o.hasOwnProperty('hasOwnProperty'); // returns false
Iterating over the properties of an object
The following example shows how to iterate over the properties of an object without executing on inherited properties. Note that the for...in
loop is already only iterating enumerable items, so one should not assume based on the lack of non-enumerable properties shown in the loop that hasOwnProperty
itself is confined strictly to enumerable items (as with Object.getOwnPropertyNames()
).
var buz = { fog: 'stack' }; for (var name in buz) { if (buz.hasOwnProperty(name)) { console.log('this is fog (' + name + ') for sure. Value: ' + buz[name]); } else { console.log(name); // toString or something else } }
Using hasOwnProperty as a property name
JavaScript does not protect the property name hasOwnProperty
; thus, if the possibility exists that an object might have a property with this name, it is necessary to use an external hasOwnProperty
to get correct results:
var foo = { hasOwnProperty: function() { return false; }, bar: 'Here be dragons' }; foo.hasOwnProperty('bar'); // always returns false // Use another Object's hasOwnProperty // and call it with 'this' set to foo ({}).hasOwnProperty.call(foo, 'bar'); // true // It's also possible to use the hasOwnProperty property // from the Object prototype for this purpose Object.prototype.hasOwnProperty.call(foo, 'bar'); // true
Note that in the last case there are no newly created objects.
Specifications
Specification |
---|
ECMAScript (ECMA-262) The definition of 'Object.prototype.hasOwnProperty' in that specification. |
Browser compatibility
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
hasOwnProperty | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 5.5 | Opera Full support 5 | Safari Full support 3 | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support 10.1 | Safari iOS Full support 1 | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
Legend
- Full support
- Full support