See http://jsfiddle.net/FDhQF/1/ for a trivial example.
What's the difference between something being undefined and something not being defined in Javascript? For instance, trying to access a property for an object (effectively, trying to access a variable) that isn't defined will return undefined. But you can also set something = undefined. When you do that, trying to access it still return undefined, but the pointer is still there. An example, as above, is how iterating over an object still goes over the property that you've (re)declared as undefined. It seems like there are two different sorts of undefined. Can anyone shed some light on the situation?