Domenic Denicola wrote:
From: Brendan Eich [[email protected]]
Yes, and I've written about why invariants matter on occasion -- perhaps you
missed that :-P.
Heh, 2008 was before my time. But generally yes, I certainly understand the
importance of invariants. I am just not sure this particular invariant is
something people actually depend on.
People do depend on this, though. Some JS users take advantage of ==, in
particular of
* null == undefined
* typeof x == typeof y
The latter makes use of knowledge that typeof's result is always of
string type.
You may argue people should always use === everywhere, but it's a fact
that == is supported *and* used.
This I guess is the heart of my question. When I said "nobody uses `==`," I should have
said "nobody writes code using `==` that depends on that logical equivalence."
False. When operand typeof-types match, == is short for === and people
use this (second bullet above is the most common case I've seen, but not
the only case).
The `typeof x == "object"&& !x => x === null` invariant I can certainly see
being used in the wild, mainly to avoid the special-caseness of `null` being an
object-according-to-`typeof`, but I can't for the life of me think of how to use the
`typeof`/`==`/`===` relation.
As I wrote last time, *we* language designers/stewards of TC39 care for
good reason.
It's not an equality, rather a two-way implication. It helps us reason about
all three of typeof, ==, and === as we evolve JS. It's not noise, and not
nothing.
My perspective is that reasoning about `==`, and even to some extent `typeof`, is not
that important, since they are both "broken."
Let's cut this thread mercifully short. Language designers tending
ECMA-262 cannot turn such a blind eye, period, full stop.
/be
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