Tab Atkins Jr. wrote:
Okay, further testing shows that my knowledge was incomplete. Null
and undefined compare as double-equal, but neither are double-equal to
other falsey values.
This is intentional, believe it or don't :-P.
In ancient days, void 0 was the only way to spell undefined, and users
immediately tested o.p != null to existing-check. There was even some
confusion where missing array elements in primordial JS evaluated to
null not undefined. Argh, I had made myself forget that, now I remember.
However, my argument stands - being undefined-specific is not
arbitrary, because that's what is actually returned by such things.
Both args without values and properties that don't exist give the
value undefined when you try to reference them.
Agree still. I do not see use-cases for including null. Maybe they
exist, though -- someone please cite some github-hosted JS.
Even the Node workaround/premature-optimization of storing null rather
than using delete doesn't argue for defaulting based on LHS value in
{null, undefined}.
Using a double-equal
check against null to test for whether something is undefined only
works because double-equal is pretty screwed up.
It is screwed up but for reasons. Bad reasons, kind of like history or
biology. Not just Homer Simpson "Life is just a bunch of things that
happen" randomness, mind you! :-P
The most principled reason I've heard, IIRC from @jashkenas, is that
null and undefined are confusingly similar, in part due to being ==.
This is true, but I still do not see actual use-cases where null is
passed into code that uses || to select a default value. Would love to
see such real-world code.
/be
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