Reprint: five methods to determine whether an object has attributes

During programming development , We often need to determine whether an object has certain properties . ad locum , We list   了 5 A way to judge the properties of an object .

1、in Operator

If the specified attribute is in the specified object or its prototype chain , be  in Operator  return  true.

usage ：

however  in Operator There is a drawback , That's it ： If the attribute comes from the prototype of the object , It will still return  true.

2、Reflect.has()  Method

Reflect.has  Method allows us to check whether the attribute is in the object . It looks like  in Operator  Work as a function .

usage ：

3、 hasOwnProperty()  Method

hasOwnProperty()  Method returns a Boolean value , Indicates whether the object has the specified property as its own property （ Instead of inheriting it ）.

It can correctly distinguish the attributes of the object itself from those of its prototype .

usage ：

But this way of writing has a drawback , That is, if the object uses Object.create(null) Create words , Then you can't use this method .

4、Object.prototype.hasOwnProperty()  Method

The solution to the previous problem is simple , We just need to use Object.prototype.hasOwnProperty. This method calls the built-in effective function directly , Skip prototype chain .

5、Object.hasOwn()  Method

Because the previous methods are not elegant ,ES2022 There is a new proposal ：Object.hasOwn

If the specified object has the specified attribute as its own attribute , be  Object.hasOwn()  Static method returns  true. If the attribute is inherited or does not exist , Then the method returns  false.

usage ：