Object.prototype.hasOwnProperty()
The hasOwnProperty() method returns a boolean value indicating whether the object has the specified property (that is, whether it has the specified key) in its own properties. In layman's terms: it is used to determine whether a property is defined in the object itself rather than inherited from the prototype chain.
grammar
obj.hasOwnProperty(prop)
The String string representation of the name, or Symbol, of the property to check for prop .- Return value Boolean
used to determine whether an object has the specified property.
example
const obj = {
};
obj.property1 = 88;
console.log(obj.hasOwnProperty('property1')); // true
console.log(obj.hasOwnProperty('toString')); // false
console.log(obj.hasOwnProperty('hasOwnProperty')); // false
Note: Even if the property's value is nullor undefined, as long as the property exists, hasOwnPropertyit will still be returned true.
o = new Object();
o.lisi = null;
o.hasOwnProperty('lisi'); // 返回 true
o.lizi = undefined;
o.hasOwnProperty('lizi'); // 返回 true
Using the hasOwnProperty method to determine whether a property exists
The following example checks whether an object o has its own property prop:
o = new Object();
o.hasOwnProperty('prop'); // 返回 false
o.prop = 'exists';
o.hasOwnProperty('prop'); // 返回 true
delete o.prop;
o.hasOwnProperty('prop'); // 返回 false
Owned and Inherited Properties
The following example demonstrates the difference between the hasOwnProperty method's treatment of owned and inherited properties:
o = new Object();
o.prop = 'exists';
o.hasOwnProperty('prop'); // 返回 true
o.hasOwnProperty('toString'); // 返回 false
o.hasOwnProperty('hasOwnProperty'); // 返回 false
Using hasOwnProperty as the property name
JavaScript does not protect hasOwnPropertythe property name, so there is a situation where hasOwnProperty is set as the function name:
var foo = {
hasOwnProperty: function() {
return false;
},
bar: 'Here be dragons'
};
Then, when using:
foo.hasOwnProperty('bar'); // 始终返回 false
To solve this situation, you can use the following two methods:
// 1. 可以直接使用原型链上真正的 hasOwnProperty 方法
({
}).hasOwnProperty.call(foo, 'bar'); // true
// 2. 使用 Object 原型上的 hasOwnProperty 属性
Object.prototype.hasOwnProperty.call(foo, 'bar'); // true
Notice, and only in the last case, no new object will be created.