I hadn't thought of it that way (comparing borks, not sql null); it does make some sense in that light (though then you should be able to compare the same NaN in two variables...).

Though that undefined === undefined works, and so does Infinity === Infinity doesn't make as much sense when thought of that way; infinities aren't all equal, and undefined isn't a single kind of value that it makes sense to compare as if it were. And to counteract the sql null viewpoint, (null === null) works.

Also:

  var x = parseInt("a");
  x === NaN // false
  alert(x); // "NaN"

doesn't make a whole lot of sense. isNaN() performs the exact same thing that === NaN implies. Especially as:

  {}.x // undefined
  {x:undefined}.x // undefined
  for(prop in {x:undefined}) alert(prop); // displays "x"
  {}.x === {x:undefined}.x // true

Meh. It's a weird language. Not intending to shoot you down; just spilling my brain into a textbox.