[WorldMaker]

Also, the "wisdom of the Ancients" in JS was to never intentionally set a value to `undefined`. While a lot of the quirks have been paved over by TC39, `undefined` was originally considered an implementation detail of the JS engine and had different semantics in different engines, especially when trying to set something to `undefined` (`myobject.field = undefined` might be equivalent to `delete myobject.field` in one engine, equivalent to setting to `null` in another engine, and its own explicit primitive value in a third, while a fourth threw an error when setting anything explicitly to undefined because it was not a value at all). Even with paved over semantics and a general convergence among JS engines (and a near monopoly of V8 in practical usage), I still find it worrisome seeing codebases that treat undefined and null as very distinct values instead of shades of gray of the same concept, because `undefined` certainly wasn't meant to be a value originally.

[recursive]

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.

[WorldMaker]

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.