A tag on the page, such as div (id= "test"), gets its js object and, var obj =
document.getElementById ("test"). I want to see the property descriptor of one of its properties, but undefined, is here to consult my predecessors.
Object.getOwnpropertyDescriptor (obj, "attributes"); undefined
tested it and found that it did return undefined . Here's my thought process:
Object.getOwnPropertyDescriptor you can see from the method name that this attribute must be the own attribute , not the attribute on the prototype chain, so is attributes not the own attribute of the dom element ? Object.hasOwnProperty to verify, and sure enough, it returns false . Since it is not an own property, Object.getOwnPropertyDescriptor returns undefined . But why not have their own attributes? Object.hasOwnProperty to test the objects on the prototype chain of obj , and returns false . dom object has done special treatment. So what if I still want to see this property descriptor? attributes is not an inherent property of obj , then I can create a js object , and then set the attributes attribute to obj.attributes . 
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