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Re: Understanding someone's code

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In article <XnsA7487B53461A9eejj99@194.109.6.166>,
Evertjan. <exxjxw.hannivoort@inter.nl.net> wrote:
> Andrew Poulos <ap_prog@hotmail.com> wrote on 30 Mar 2017 in 
> comp.lang.javascript:
> 
> > On 30/03/2017 3:26 PM, Andrew Poulos wrote:
> >> I'm looking through some code I found online and one bit has this
> >>
> >> function k() {
> >>   var a;
> >>   if (b.onScroll) b.onScroll();
> >>   b.getPageInView && (a = b.getPageInView()) && (F = a,
> >> document.getElementById("pageNumber").value = a);
> >> }
> >>
> >> which has me confused. Is the line
> >>
> >>   b.getPageInView && (a = b.getPageInView()) && (F = a,
> >> document.getElementById("pageNumber").value = a);
> >>
> >> equivalent to
> >>
> >> if (b.getPageInView) {
> >>   a = b.getPageInView();
> >>   F = a;
> >>   document.getElementById("pageNumber").value = a;
> >> }
> > 
> > Or  should I have said, is equivalent to
> > 
> > if (b.getPageInView) {
> >    a = b.getPageInView();
> >    if (a) {
> >      F = a;
> >      document.getElementById("pageNumber").value = a;
> >    }
> >}
> 
> No.

Why not? It looks equivalent to me, in that specific case. If you believe
it to be a wrong interpretation of the original code, why not provide
a better one, instead of the unrelated and simple example below?

> The right side of && is only executed 
> if and after[!] execution of the left side has returned true.

Yes, that's right. Which is what the OP's "if" statements are doing.
Remember that in the original code, the result of the X && Y && Z
expression is discarded, not assigned.

> So:
> 
> 'use strict'
> let a = 4;
> document.write( a ); //  4
> document.write( a && 15-15 ); //  0
> document.write( a ); //  4
> document.write( (a=0) && (a=1) ); //  0
> document.write( a ); //  0
> document.write( (a=17) && (a=0) && (a=13) ); //  0
> document.write( a ); //  0

All true, but not relevant to the original example.

Cheers
Tony
-- 
Tony Mountifield
Work: tony@softins.co.uk - http://www.softins.co.uk
Play: tony@mountifield.org - http://tony.mountifield.org

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Understanding someone's code Andrew Poulos <ap_prog@hotmail.com> - 2017-03-30 15:26 +1100
  Re: Understanding someone's code Andrew Poulos <ap_prog@hotmail.com> - 2017-03-30 18:48 +1100
    Re: Understanding someone's code "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2017-03-30 12:07 +0200
      Re: Understanding someone's code tony@mountifield.org (Tony Mountifield) - 2017-03-30 11:43 +0000
        Re: Understanding someone's code "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2017-03-30 14:00 +0200
          Re: Understanding someone's code tony@mountifield.org (Tony Mountifield) - 2017-03-30 13:44 +0000
            Re: Understanding someone's code "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2017-03-30 19:07 +0200
    Re: Understanding someone's code JJ <jj4public@vfemail.net> - 2017-03-30 18:58 +0700
      Re: Understanding someone's code Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-03-30 18:13 +0200
    Re: Understanding someone's code Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-03-30 18:13 +0200
      Re: Understanding someone's code John G Harris <niam@jghnorth.org.uk.invalid> - 2017-03-31 10:30 +0100
        Re: Understanding someone's code Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-04-02 14:41 +0200
          Re: Understanding someone's code John G Harris <niam@jghnorth.org.uk.invalid> - 2017-04-02 19:05 +0100
            Re: Understanding someone's code Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-04-10 05:00 +0200
              Re: Understanding someone's code John G Harris <niam@jghnorth.org.uk.invalid> - 2017-04-10 10:03 +0100

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