Toggling a string

[Dr John Stockton]

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.

--
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[Matthew Lock]

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';

[RobG]

Matthew Lock wrote:

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';

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

[Matthew Lock]

RobG wrote:

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

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.

[Michael Winter]

Matthew Lock wrote:

[snip]

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';

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.

[Dr John Stockton]

JRS: In article <6t*****************@news.optus.net.au>, dated Mon, 14
Feb 2005 04:06:26, seen in news:comp.lang.javascript, RobG
<rg***@iinet.net.auau> posted :

Matthew Lock wrote:

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';

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'.

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 ©
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[Matthew Lock]

Michael Winter wrote:

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

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