Benefit of using Object.hasOwnProperty vs. testing if a property is undefined

Question

Since hasOwnProperty has some caveats and quirks (window / extensive use in Internet Explorer 8 issues, etc.):

Is there any reason to even use it

Answer 1

hasOwnProperty does not check for undefined values. It only checks if a property is assigned to the object even if is undefined:

var obj = { a : undefined };
obj.hasOwnProperty("a") // true
obj.a === undefined     // true
obj.hasOwnProperty("b") // false
obj.b === undefined     // true