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Re: Element visible

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Andrew Poulos wrote:

>> Andrew Poulos wrote:
>>> And also ignoring other instances where its positioned off screen.
>
> Media queries can turn things on or off. User actions can turn things on
> or off. A user turns a thing on and subsequently a media query turns it
> off. If I'm tracking the user interaction the thing is on when in fact
> its not. So then to know if the thing is on or off I need to either
> track media queries and user interaction or, perhaps, I can just ask it,
> but what would I test for?

Good question.

I can only see two possibilities, other than those that you have excluded, 
that can cause an element to be not visible:

One, the element may not be part of a real document but exist only as 
element object in memory.  In that case the value of the “parentNode” 
property of that object would be “null” or at least a false-value because it 
has no parent node.

However, it may also be a descendent node of a node that only exists in 
memory.  In that case the former’s “parentNode” property value would not be 
“null”, but following up to the next ancestor until the “parentNode” 
property value of the target node is “null” should be sufficient in most 
cases.

Yet, with this approach there is a potential for false positives because the 
root element node’s “parentNode” property value is always “null” (or a 
false-value).  I have just found out (in Chromium 34) that even the value of 
the “ownerDocument” property of a node object can be not “null” if the 
represented node was previously part of a real (HTML5) document.  So I have 
yet to find a reliable test for this possibility.

Two, the element may be part of the document but, as you indicated, 
stylesheet declarations prevent it from being visible.  In that case you 
need to retrieve the computed style of the element and check if any of that 
style’s properties that pertain to display, or a combination of them, could 
cause the element to be not visible.  You may also need to consider the 
style of the element’s ancestors, for example in the case of the “display” 
property.

There is a lot of information about this problem on the Web.  Apparently 
none of the existing approaches cover the full range of possibilities.
See the CSS specifications and the pertaining newsgroup for details.

-- 
PointedEars
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Element visible Andrew Poulos <ap_prog@hotmail.com> - 2014-07-09 10:09 +1000
  Re: Element visible Andrew Poulos <ap_prog@hotmail.com> - 2014-07-09 13:32 +1000
    Re: Element visible "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2014-07-09 09:54 +0200
    Re: Element visible Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-07-09 11:18 +0200
      Re: Element visible Andrew Poulos <ap_prog@hotmail.com> - 2014-07-09 23:17 +1000
        Re: Element visible John Harris <niam@jghnorth.org.uk.invalid> - 2014-07-09 16:08 +0100
      Re: Element visible Andrew Poulos <ap_prog@hotmail.com> - 2014-07-10 10:07 +1000
        Re: Element visible "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2014-07-10 09:15 +0200
          Re: Element visible "Jukka K. Korpela" <jkorpela@cs.tut.fi> - 2014-07-10 10:45 +0300
            Re: Element visible Andrew Poulos <ap_prog@hotmail.com> - 2014-07-10 22:13 +1000
              Re: Element visible "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2014-07-10 14:31 +0200
                Re: Element visible Scott Sauyet <scott.sauyet@gmail.com> - 2014-07-10 13:35 -0700
                Re: Element visible "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2014-07-11 00:23 +0200
                Re: Element visible Scott Sauyet <scott.sauyet@gmail.com> - 2014-07-12 20:09 -0700
                Re: Element visible "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2014-07-13 09:07 +0200
          Re: Element visible John Harris <niam@jghnorth.org.uk.invalid> - 2014-07-10 10:46 +0100
        Re: Element visible Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-07-10 12:10 +0200
          Re: Element visible Andrew Poulos <ap_prog@hotmail.com> - 2014-07-14 13:00 +1000
          Re: Element visible Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-07-15 15:08 +0200

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