Toggling a string

[Dr John Stockton]

I see, quite often, code like

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

which is cumbersome even with the substitution T = tmp.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.

 

[Matthew Lock]

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

tmp.style.display = tmp.style.display == 'block' ? 'none' :
'block';

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

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

 

[RobG]

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

tmp.style.display = tmp.style.display == 'block' ? 'none' :
'block';

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

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

Have a read of Mike Winter's post:

news://inetbws1.citec.qld.gov.au:119/[email protected]

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

 

[Matthew Lock]

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.style.display" twice, this:

var t = tmp.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.style;
s.display = ('' == s.display) ? 'none' : '';

OR

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

s.display = dP[s.display];

A very interesting idea, John.

Mike

 

[Dr John Stockton]

JRS: In article <[email protected]>, dated Mon, 14
Feb 2005 04:06:26, seen in RobG

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

tmp.style.display = tmp.style.display == 'block' ? 'none' :
'block';

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

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

Have a read of Mike Winter's post:

news://inetbws1.citec.qld.gov.au:119/[email protected]
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.

 

[Matthew Lock]

var t = tmp.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.