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Podsumowanie
Metoda hasOwnProperty()
zwraca wartość true jeśli obiekt, na którym została wywołana posiada konkretną własność.
Składnia
obj.hasOwnProperty(prop)
Parametry
prop
- Nazwa własności do przetestowania.
Opis
Każdy obiekt pochodzący od Object
dziedziczy metodę hasOwnProperty
. Może być ona użyta do stwierdzenia czy obiekt posiada określoną własność, jako bezpośrednią (direct) własność. W przeciwieństwie do operatora in
, metoda hasOwnProperty
nie sprawdza w głąb łańcucha własności obietu.
Przykłady
Example: 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.prop = 'exists'; function changeO() { o.newprop = o.prop; delete o.prop; } o.hasOwnProperty('prop'); // returns true changeO(); o.hasOwnProperty('prop'); // returns false
Example: Direct versus 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
Example: Iterating over the properties of an object
The following example shows how to iterate over the properties of an object without executing on inherit 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)) { alert('this is fog (' + name + ') for sure. Value: ' + buz[name]); } else { alert(name); // toString or something else } }
Example: hasOwnProperty
as a property
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 | Status | Comment |
---|---|---|
ECMAScript 3rd Edition. | Standard | Initial definition. Implemented in JavaScript 1.5. |
ECMAScript 5.1 (ECMA-262) The definition of 'Object.prototype.hasOwnProperty' in that specification. |
Standard | |
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'Object.prototype.hasOwnProperty' in that specification. |
Standard |
Browser compatibility
Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|
Basic support | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|---|
Basic support | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |