javascript - Is there any way to distinguish between an unset property and a property set to undefined?

Say I have the object testObject = {a: undefined}. If I then console.log(testObject.a), I get undefined. But the same happens if I console.log(testObject.b), which doesn't exist. Is there any way in JavaScript to distinguish between a and b here? I ask mostly out of curiosity, I have no use case.

Answer

hasOwnProperty() method returns a boolean indicating whether the object has the specified property as own (not inherited) property.

In given case -

  testObject = {a: undefined};

  testObject.hasOwnProperty('a') //true
  testObject.hasOwnProperty('b') //false