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Groups > comp.lang.javascript > #39968

Re: Understanding &&

From Arno Welzel <usenet@arnowelzel.de>
Newsgroups comp.lang.javascript
Subject Re: Understanding &&
Date 2021-04-18 00:40 +0200
Message-ID <ie16fpFavc9U1@mid.individual.net> (permalink)
References <U_CdnQWSXulHj-T9nZ2dnUU7-evNnZ2d@westnet.com.au> <slrns7ishn.4j8.jon+usenet@raven.unequivocal.eu> <87wnt2e06e.fsf@bsb.me.uk> <slrns7jb5v.4j8.jon+usenet@raven.unequivocal.eu> <87mttydm95.fsf@bsb.me.uk>

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Ben Bacarisse:

> Jon Ribbens <jon+usenet@unequivocal.eu> writes:
> 
>> On 2021-04-16, Ben Bacarisse <ben.usenet@bsb.me.uk> wrote:
>>> Jon Ribbens <jon+usenet@unequivocal.eu> writes:
>>>> You most often see this sort of thing in JavaScript that was
>>>> automatically generated by a compiler (either because the original
>>>> source was in something else like TypeScript or a more modern version
>>>> of JavaScript or because the author wanted to compress/minify the
>>>> script), but human beings are also quite capable of writing hard-to-read
>>>> code like this.
>>>
>>> Is that specifically when the right-hand operand is an assignment
>>> expression?  I don't find that hard to read but then I'm used to
>>> assignment being and expression so it seems like a natural extension of
>>> the more frequently seen uses of &&.
>>
>> I mean where it's an expression being abused as a control flow
>> mechanism.
> 
> If readability is not the problem I'm not sure what constitutes abuse.

Abuse is to use things for something which they are not meant to be
used. An *expression* is called so because you *express* something like

x = a && b;

Nobody would expect that this *expression* will cause parts of the code
to get executed or not like in this example:

x = a && (b=5);

It's not just a "readability problem". It's relying on side effects like
that in a && b the "b" part will not get exectued if "a" is false. But
this is just a convention and nothing obvious.

> Is it just a rule of yours to keep these two things entirely separate?
> Maybe some uses are acceptable and don't constitute abuse?  Is any

I see this as "abuse" as well.

> reliance on short-circuit evaluation in an expression an abuse?  If so,
> does that extend to '??' and '?.'?  (That's not easy to make clear in
> typing but I hope you know what I mean.)

The ??= operator was *intentionally* designed to work this way.

x ??= y;

will assign y to x only if x is not null or undefined. There is no
surprise here what to expect from this expression.

However:

x = a && (b=5);

Will assing something to x and *maybe* to b as well if a is not false.

To understand this you need not only to know what the operator && does
but also that it is evaluated from left to right and that if the left
part is false the right part won't be used at all.

> I only suggested that assignment might be where it crosses the line for
> you because I think that's where the line is for a lot of people, but it
> sounds like go further than that.
> 
> I go the other way.  Statements (most of them at least) are just wasted
> expression opportunities.  It's less noticeable in ECMAScript, than in
> many other languages, but it still bugs me every now and then.

Well - if you feel comfortable with this, you can but a whole program
into a a few expressions without barely any statement at all. But this
has nothing to do with good code style or anything which should be
recommended as good practice.


-- 
Arno Welzel
https://arnowelzel.de

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Thread

Understanding && Andrew Poulos <ap_prog@hotmail.com> - 2021-04-16 14:30 +1000
  Re: Understanding && Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-04-16 11:00 +0100
  Re: Understanding && Jon Ribbens <jon+usenet@unequivocal.eu> - 2021-04-16 11:17 +0000
    Re: Understanding && Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-04-16 16:09 +0100
      Re: Understanding && Jon Ribbens <jon+usenet@unequivocal.eu> - 2021-04-16 15:26 +0000
        Re: Understanding && Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-04-16 21:09 +0100
          Re: Understanding && Jon Ribbens <jon+usenet@unequivocal.eu> - 2021-04-16 21:06 +0000
            Re: Understanding && Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-04-17 02:01 +0100
              Re: Understanding && The Natural Philosopher <tnp@invalid.invalid> - 2021-04-17 08:33 +0100
              Re: Understanding && John G Harris <niam@jghnorth.org.uk.invalid> - 2021-04-17 12:06 +0100
                Re: Understanding && The Natural Philosopher <tnp@invalid.invalid> - 2021-04-17 14:13 +0100
                Re: Understanding && Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-04-17 15:50 +0100
              Re: Understanding && Jon Ribbens <jon+usenet@unequivocal.eu> - 2021-04-17 15:21 +0000
                Re: Understanding && Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-04-17 23:46 +0100
                Re: Understanding && Jon Ribbens <jon+usenet@unequivocal.eu> - 2021-04-17 23:46 +0000
                Re: Understanding && Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-04-18 23:59 +0100
                Re: Understanding && Jon Ribbens <jon+usenet@unequivocal.eu> - 2021-04-19 13:56 +0000
                Re: Understanding && Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-04-19 23:08 +0100
                Re: Understanding && Jon Ribbens <jon+usenet@unequivocal.eu> - 2021-04-19 22:52 +0000
                Re: Understanding && Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-04-20 01:23 +0100
                Re: Understanding && Jon Ribbens <jon+usenet@unequivocal.eu> - 2021-04-20 01:08 +0000
              Re: Understanding && Arno Welzel <usenet@arnowelzel.de> - 2021-04-18 00:49 +0200
                Re: Understanding && Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-04-18 17:26 +0100
          Re: Understanding && Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2021-04-17 17:05 +0200
            Re: Understanding && Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-04-17 23:04 +0100
              Re: Understanding && Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2021-04-18 00:48 +0200
                Re: Understanding && Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-04-18 17:13 +0100
                Re: Understanding && Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2021-04-19 21:58 +0200
            Re: Understanding && John G Harris <niam@jghnorth.org.uk.invalid> - 2021-04-18 18:20 +0100
          Re: Understanding && Arno Welzel <usenet@arnowelzel.de> - 2021-04-18 00:40 +0200
            Re: Understanding && Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-04-18 00:14 +0100
              Re: Understanding && Jon Ribbens <jon+usenet@unequivocal.eu> - 2021-04-18 00:01 +0000
                Re: Understanding && Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-04-18 17:44 +0100
                Re: Understanding && Jon Ribbens <jon+usenet@unequivocal.eu> - 2021-04-18 17:51 +0000
              Re: Understanding && Arno Welzel <usenet@arnowelzel.de> - 2021-04-19 13:41 +0200
                Re: Understanding && John G Harris <niam@jghnorth.org.uk.invalid> - 2021-04-19 15:02 +0100
                Re: Understanding && The Natural Philosopher <tnp@invalid.invalid> - 2021-04-20 17:40 +0100
                Re: Understanding && John G Harris <niam@jghnorth.org.uk.invalid> - 2021-04-20 18:19 +0100
                Re: Understanding && The Natural Philosopher <tnp@invalid.invalid> - 2021-04-21 10:11 +0100
                Re: Understanding && John G Harris <niam@jghnorth.org.uk.invalid> - 2021-04-21 19:46 +0100
                Re: Understanding && The Natural Philosopher <tnp@invalid.invalid> - 2021-04-22 13:48 +0100
                Re: Understanding && Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-04-19 21:28 +0100
                Re: Understanding && Jon Ribbens <jon+usenet@unequivocal.eu> - 2021-04-19 21:56 +0000
                Re: Understanding && Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-04-19 23:13 +0100

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