Default operator strawman - ||| rather than ??
brendan at mozilla.org
Wed Jun 13 11:18:52 PDT 2012
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
> 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.
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