Small Proposal "!in"

Alex Vincent ajvincent at
Wed Jul 11 15:24:23 UTC 2018

> ---------- Forwarded message ----------
> From: Andrea Giammarchi <andrea.giammarchi at>
> To: Jordan Harband <ljharb at>
> Cc: "es-discuss at" <es-discuss at>
> Bcc:
> Date: Wed, 11 Jul 2018 16:23:03 +0200
> Subject: Re: Small Proposal "!in"
> and, as previously mentioned, `!obj.x` might have side effects through the
> accessor, as example in every lazily defined property that would be early
> defined (or anything else behind a getter that could do more than just
> telling the property is there and it's not truthy).

Peanut gallery observation: I personally think !in is a Really Bad Idea, or
at least I'm not convinced that it's particularly useful.  If it is useful,
then let one of the transpiling languages like CoffeeScript or TypeScript
demonstrate it first.

Also, there's the little matter of pronunciation.  I admit to a bit of
snarkiness when I first saw this proposal, but I didn't expect it to have
any traction.  So I'll just say it:  do we really want JavaScript to be a
"bangin' " language?


"The first step in confirming there is a bug in someone else's work is
confirming there are no bugs in your own."
-- Alexander J. Vincent, June 30, 2001
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