JS中Testing Properties如何判断属性是否在对象里

这篇文章主要为大家展示了“JS中Testing Properties如何判断属性是否在对象里”，内容简而易懂，条理清晰，希望能够帮助大家解决疑惑，下面让小编带领大家一起研究并学习一下“JS中Testing Properties如何判断属性是否在对象里”这篇文章吧。

Testing Properties

To check whether an object has a property with a given name. You can do this with the in operator, with the hasOwnProperty() and propertyIsEnumerable() methods,

在JS中判断一个对象是否包含某个属性，可以使用 in，hasOwnProperty() and propertyIsEnumerable()

or simply by querying the property.

或者直接使用查询属性。

in--It returns true if the object has an own property or an inherited property 

用In，当前对象存在或者有继承，就返回true。

hasOwnProperty() --To test whether that object has an own property with the given name. It returns false for inherited properties

用hasOwnProperty() ，只关心本对象，不关心继承来的属性。

propertyIsEnumerable()--The propertyIsEnumerable() refines the hasOwnProperty() test. It returns true only if the named property is an own property and its enumerable attribute is true.

用propertyIsEnumerable() ，和hasOwnProperty() 这个类似，只是要求 属性可枚举。

 Instead of using the in operator  it is often sufficient to simply query the property and use !== to make sure it is not undefined

 o.x !== undefined; // true: o has a property x

替代In的最简单办法就是  query   +    ！==Undefined

in can distinguish between properties that do not exist and properties that exist but have been set to undefined.

in 有个好处就是还能区分到底属性的值是undefined还是本身就不存在。

以上是“JS中Testing Properties如何判断属性是否在对象里”这篇文章的所有内容，感谢各位的阅读！相信大家都有了一定的了解，希望分享的内容对大家有所帮助，如果还想学习更多知识，欢迎关注编程网行业资讯频道！