Toggling a string

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  • Dr John Stockton
    #1

    Toggling a string


    I see, quite often, code like

    if (tmp[i].style.display == 'none')
    tmp[i].style.display = 'block';
    else
    if (tmp[i].style.display == 'block')
    tmp[i].style.display = 'none';
    or
    if (tmp[i].style.display == 'none')
    tmp[i].style.display = 'block';
    else
    tmp[i].style.display = 'none';

    which is cumbersome even with the substitution T = tmp[i].style .

    Consider

    X = {'none':'block' , 'block':'none' /* , 'undefined' : 'none' */ }

    T = F.X0 ; T.value = X[T.value]

    where of course X is set once and for all. When the second line is
    executed, F.X0.value is toggled. If the X-line comment symbols are
    removed, false values are corrected after TWO goes.

    In practice, X should be spelt blockORnone or similar.

    --
    © John Stockton, Surrey, UK. ?@merlyn.demon. co.uk Turnpike v4.00 IE 4 ©
    <URL:http://www.jibbering.c om/faq/> JL/RC: FAQ of news:comp.lang. javascript
    <URL:http://www.merlyn.demo n.co.uk/js-index.htm> jscr maths, dates, sources.
    <URL:http://www.merlyn.demo n.co.uk/> TP/BP/Delphi/jscr/&c, FAQ items, links.
    Tags: None
    • Matthew Lock
      #2
      Re: Toggling a string

      Interesting. I would usually abbreviate the first way to this:

      tmp[i].style.display = tmp[i].style.display == 'block' ? 'none' :
      'block';

      Or if you didn't want to repeat "tmp[i].style.display" twice, this:

      var t = tmp[i].style.display;
      t = t == 'block' ? 'none' : 'block';

        Comment

        • RobG
          #3
          Re: Toggling a string

          Matthew Lock wrote:[color=blue]
          > Interesting. I would usually abbreviate the first way to this:
          >
          > tmp[i].style.display = tmp[i].style.display == 'block' ? 'none' :
          > 'block';
          >
          > Or if you didn't want to repeat "tmp[i].style.display" twice, this:
          >
          > var t = tmp[i].style.display;
          > t = t == 'block' ? 'none' : 'block';
          >[/color]

          Have a read of Mike Winter's post:

          news://inetbws1.citec.qld.gov.au:119...oglegroups.com

          to discover why toggling between 'block' and 'none' is not
          recommended. It's probably better to go between '' and 'none'.

          --
          Rob

            Comment

            • Matthew Lock
              #4
              Re: Toggling a string


              RobG wrote:[color=blue]
              > to discover why toggling between 'block' and 'none' is not
              > recommended. It's probably better to go between '' and 'none'.[/color]

              Yeah I am aware that it requires the toggled element to already have
              display: none or display: block as part of its style. Good point.

                Comment

                • Michael Winter
                  #5
                  Re: Toggling a string

                  Matthew Lock wrote:

                  [snip]
                  [color=blue]
                  > Or if you didn't want to repeat "tmp[i].style.display" twice, this:
                  >
                  > var t = tmp[i].style.display;
                  > t = t == 'block' ? 'none' : 'block';[/color]

                  However, that would fail. You would assign a string value to t, not a
                  reference to the display property. Assigning to t a second time would
                  update that variable, nothing more.

                  What you could do is store a reference to the style object:

                  var s = tmp[i].style;
                  s.display = ('' == s.display) ? 'none' : '';

                  OR

                  var dP = {'' : 'none', 'none' : ''};

                  s.display = dP[s.display];

                  A very interesting idea, John.

                  Mike

                  --
                  Michael Winter
                  Replace ".invalid" with ".uk" to reply by e-mail.

                    Comment

                    • Dr John Stockton
                      #6
                      Re: Toggling a string

                      JRS: In article <6tVPd.532$Ud4. 41794@news.optu s.net.au>, dated Mon, 14
                      Feb 2005 04:06:26, seen in news:comp.lang. javascript, RobG
                      <rgqld@iinet.ne t.auau> posted :[color=blue]
                      >Matthew Lock wrote:[color=green]
                      >> Interesting. I would usually abbreviate the first way to this:
                      >>
                      >> tmp[i].style.display = tmp[i].style.display == 'block' ? 'none' :
                      >> 'block';
                      >>
                      >> Or if you didn't want to repeat "tmp[i].style.display" twice, this:
                      >>
                      >> var t = tmp[i].style.display;
                      >> t = t == 'block' ? 'none' : 'block';
                      >>[/color]
                      >
                      > Have a read of Mike Winter's post:
                      >
                      >news://inetbws1.citec.qld.gov.au:119...000cwo.googleg
                      >roups.com
                      >
                      > to discover why toggling between 'block' and 'none' is not
                      > recommended. It's probably better to go between '' and 'none'.[/color]

                      But that does not just toggle between those two; it converts anything
                      but 'block' to 'block' and 'block' to 'none'.



                      ==

                      When you find a relevant article on the Web, it's best to include its
                      essence, as well as its URL, in News; some of us read news off-line.
                      Copy'n'paste should be able to extract something suitable from a well-
                      written item.

                      --
                      © John Stockton, Surrey, UK. ?@merlyn.demon. co.uk Turnpike v4.00 IE 4 ©
                      <URL:http://www.jibbering.c om/faq/> JL/RC: FAQ of news:comp.lang. javascript
                      <URL:http://www.merlyn.demo n.co.uk/js-index.htm> jscr maths, dates, sources.
                      <URL:http://www.merlyn.demo n.co.uk/> TP/BP/Delphi/jscr/&c, FAQ items, links.

                        Comment

                        • Matthew Lock
                          #7
                          Re: Toggling a string


                          Michael Winter wrote:[color=blue][color=green]
                          > > var t = tmp[i].style.display;
                          > > t = t == 'block' ? 'none' : 'block';[/color]
                          >
                          > However, that would fail. You would assign a string value to t, not a[/color]
                          [color=blue]
                          > reference to the display property. Assigning to t a second time would[/color]
                          [color=blue]
                          > update that variable, nothing more.[/color]

                          You're right. That'll learn me to post code without testing it.

                            Comment

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