There has been no version of javascript where it was practical to avoid setting a variable to null. As far as I know, things like these would always do it.
var x = {}.foo;
var y = (function() {})();
These are contrived examples, but they represent things done by very reasonable code. There are all kinds of ways that `undefined` can get assigned into a variable. It's inevitable that those cases would have to be handled.
I'm saying it impractical to consider `null` and `undefined` as different "values" in JS. `undefined` was originally built to be a "thrown" exception built for a language without thrown exceptions. It wasn't intended to be a placeholder value like null is. The language today makes it possible, you can today write `var x = undefined` and expect things not to blow up or behave all that differently/quirkily between browsers and browser modes. I'm still going to be worried/skeptical of any code that intentionally uses patterns like that of setting objects and properties explicitly to `undefined` and treats that as a different value from `null`.
Yes, you have to handle cases where things are undefined, but I'd be wary of handling them too dissimilarly to where things are null, because `undefined` was not designed to be "Null 2: Electric Boogaloo", it was designed to be "404 Item Not Found Exception" in the time before JS had real exceptions.
