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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

prop
The String name or symbol of the property to test.

Return value

A Boolean indicating whether or not the object has the specified property as own property.

Description

Every object descended from Object inherits 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 down the object's prototype chain.

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 Status Comment
ECMAScript 3rd Edition (ECMA-262) 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  
ECMAScript Latest Draft (ECMA-262)
The definition of 'Object.prototype.hasOwnProperty' in that specification.
Draft  

Browser compatibility

Update compatibility data on GitHub
DesktopMobileServer
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidiOS SafariSamsung InternetNode.js
Basic supportChrome Full support YesEdge Full support YesFirefox Full support 1IE Full support YesOpera Full support YesSafari Full support YesWebView Android Full support YesChrome Android Full support YesEdge Mobile Full support YesFirefox Android Full support 4Opera Android Full support YesSafari iOS Full support YesSamsung Internet Android Full support Yesnodejs Full support Yes

Legend

Full support  
Full support

 

 

Polyfill

//github FabioVergani / js-Polyfill_Object-hasOwnProperty

//#Polyfill

/*
simple:
Object.prototype.hasOwnProperty||(Object.prototype.hasOwnProperty=function(x){var o,e=this,p=String(x);return p in e && (o=e.__proto__||e.constructor.prototype,(p in o ===false)||e[p]!== o[p])});
*/

//Advanced:
(function(w){
    var isFunction=w.isFunction||(w.isFunction=function(x){return typeof(x)==='function'}),
    has=w.has||(w.has=function(o,p){var e=p in o;return {value:e && (e=o[p]) && true,refer:e,valueOf:function(){return this.value}}}),
    Polyfill=w.PolyfillMethod||(w.PolyfillMethod=function(o,p,x){var e=has(o,p);if(e && (e=isFunction(e.refer))===false){o[p]=x};return e}),
    theProto=w.Object.prototype;

    Polyfill(theProto,'hasOwnProperty',function(x){var o,e=this,p=String(x);return p in e && (o=e.__proto__||e.constructor.prototype,(p in o ===false)||e[p]!== o[p])});

})(window);




/*
var obj1={a:1,b:false}, obj2=Object.create(obj1);
obj2.a=2;
obj2.c='yeah';
//Polyfilled & Native:
console.dir([
obj1.hasOwnProperty('a'),//true
obj1.hasOwnProperty('b'),//true
obj1.hasOwnProperty('c'),//false
obj2.hasOwnProperty('a'),//true
obj2.hasOwnProperty('b'),//false
obj2.hasOwnProperty('c')//true
]);
Object.prototype.hasOwnProperty.call(Object.create(null),'a')//false
*/

 

See also

Document Tags and Contributors

Cập nhật lần cuối bởi: FabioVergani,