How Does JavaScript Call Forth CSS??

[Prisoner at War]

Okay, Folks,

I guess my real burning concern all along is a "high-level" one: just
how does JavaScript interact with CSS?

Right now, my newbie self only knows JavaScript and CSS to *co-
exist*...but I'm beginning to get the sense that they actually
interact -- or, perhaps more precisely, JavaScript acts upon CSS...but
how, exactly??

I see how JavaScript acts upon HTML, but I'm not so sure where
JavaScript acts upon CSS...moreover, I want to see where they could
create whole new browsing experiences, beyond simply new text and new
images (though I'm only just beginning at the level of new ways of
presenting text and images)....

How do I go about all this?? Ugh, I hope all those $$$ worth of books
will help...so far, I'm learning very basic things which I actually
wouldn't use (though the learning itself is fun), while the things I
would like to do, I either don't have the technical know-how for it or
I don't have the creative imagination to bring together what little I
do know -- sigh!!

[Nik Coughlin]

Re: How Does JavaScript Call Forth CSS??

"Prisoner at War" <prisoner_at_wa r@yahoo.comwrot e in message
news:c86208c9-45fb-4419-acb6-6d62c94d4ef0@m4 4g2000hsc.googl egroups.com...

>
Okay, Folks,
>
I guess my real burning concern all along is a "high-level" one: just
how does JavaScript interact with CSS?
>
Right now, my newbie self only knows JavaScript and CSS to *co-
exist*...but I'm beginning to get the sense that they actually
interact -- or, perhaps more precisely, JavaScript acts upon CSS...but
how, exactly??
>
I see how JavaScript acts upon HTML, but I'm not so sure where
JavaScript acts upon CSS...moreover, I want to see where they could
create whole new browsing experiences, beyond simply new text and new
images (though I'm only just beginning at the level of new ways of
presenting text and images)....
>
How do I go about all this?? Ugh, I hope all those $$$ worth of books
will help...so far, I'm learning very basic things which I actually
wouldn't use (though the learning itself is fun), while the things I
would like to do, I either don't have the technical know-how for it or
I don't have the creative imagination to bring together what little I
do know -- sigh!!

Basically, you get the element in Javascript, and set its style property.

<div id="content">bl ah</div>

JavaScript:

var contentDiv = document.getEle mentById( "content" );
contentDiv.styl e.marginLeft = "1em";

Generally (there may be exceptions but I'm not aware of any) the property of
the object corresponds to the name of the CSS property but camel cased.

[Jeremy J Starcher]

Re: How Does JavaScript Call Forth CSS??

[Cross-posting snipped.]

On Sat, 26 Apr 2008 16:53:33 -0700, Prisoner at War wrote:

Okay, Folks,
>
I guess my real burning concern all along is a "high-level" one: just
how does JavaScript interact with CSS?
>
Right now, my newbie self only knows JavaScript and CSS to *co-
exist*...but I'm beginning to get the sense that they actually interact
-- or, perhaps more precisely, JavaScript acts upon CSS...but how,
exactly??
>
I see how JavaScript acts upon HTML, but I'm not so sure where
JavaScript acts upon CSS...moreover, I want to see where they could
create whole new browsing experiences, beyond simply new text and new
images (though I'm only just beginning at the level of new ways of
presenting text and images)....

Javascript is a programming language. A simple but useful one.
Javascript, *BY ITS SELF* can not interact with anything.

Style sheets are a set of hints that direct a user agent over how
information should be displayed.

Both Javascript and CSS co-exist in the user agent, typically a web
browser.

(In addition there is a third important player to this game called the
DOM [Document Object Model]. The DOM gives Javascript a way to interact
with the host environment.)

How do I go about all this?? Ugh, I hope all those $$$ worth of books
will help...so far, I'm learning very basic things which I actually
wouldn't use (though the learning itself is fun), while the things I
would like to do, I either don't have the technical know-how for it or I
don't have the creative imagination to bring together what little I do
know -- sigh!!

I don't know any of the Javascript books, but I don't hear any of them
mentioned highly around here. I've learned a lot by lurking the
newsgroup here and the FAQ's.

Javascript may call DOM functions. Those functions, in turn, may update
the 'page' by replacing elements, adding elements, moving or unhiding.
In short, making a site interactive.


Start off reading the group's FAQ. That will give you a good solid
background in some of the more important aspects of Javascript.


When Googling for example code, keep in mind that 90% of everything is
crap. I got bit pretty heavily by learning from some bad examples and
put together a guide to help others avoid my mistake. Might help you.

http://www.mopedepot.com/jjs/HowToRecognizeBadJavascriptCode.html

(Hmmm.. I still haven't uploaded the final version of that. That one is
fairly good though.)

[Ben C]

Re: How Does JavaScript Call Forth CSS??

On 2008-04-27, Nik Coughlin <nrkn.com@gmail .comwrote:

"Prisoner at War" <prisoner_at_wa r@yahoo.comwrot e in message
news:c86208c9-45fb-4419-acb6-6d62c94d4ef0@m4 4g2000hsc.googl egroups.com...

>>
>Okay, Folks,
>>
>I guess my real burning concern all along is a "high-level" one: just
>how does JavaScript interact with CSS?

[...]

Basically, you get the element in Javascript, and set its style property.
>
><div id="content">bl ah</div>
>
JavaScript:
>
var contentDiv = document.getEle mentById( "content" );
contentDiv.styl e.marginLeft = "1em";
>
Generally (there may be exceptions but I'm not aware of any) the property of
the object corresponds to the name of the CSS property but camel cased.
>

Yes. Another way to do it is to change the class attributes of elements
with setAttribute.

Then you can organize the styles in style sheets rather than packing
them all into the elements' style attributes, and just switch the
elements' classes so they get selected by different selectors.

This kind of thing:

..active
{
border: 2px solid red;
background-color: yellow;
color: black;
etc.
..
}

contentDiv.setA ttribute("class ", "active")

[Nik Coughlin]

Re: How Does JavaScript Call Forth CSS??

Ben C wrote:

On 2008-04-27, Nik Coughlin <nrkn.com@gmail .comwrote:

>"Prisoner at War" <prisoner_at_wa r@yahoo.comwrot e in message
>news:c86208c 9-45fb-4419-acb6-6d62c94d4ef0@m4 4g2000hsc.googl egroups.com...

>>>
>>Okay, Folks,
>>>
>>I guess my real burning concern all along is a "high-level" one:
>>just how does JavaScript interact with CSS?

[...]

>Basically, you get the element in Javascript, and set its style
>property.
>>
><div id="content">bl ah</div>
>>
>JavaScript:
>>
>var contentDiv = document.getEle mentById( "content" );
>contentDiv.sty le.marginLeft = "1em";
>>
>Generally (there may be exceptions but I'm not aware of any) the
>property of the object corresponds to the name of the CSS property
>but camel cased.
>>

>
Yes. Another way to do it is to change the class attributes of
elements with setAttribute.
>
Then you can organize the styles in style sheets rather than packing
them all into the elements' style attributes, and just switch the
elements' classes so they get selected by different selectors.
>
This kind of thing:
>
.active
{
border: 2px solid red;
background-color: yellow;
color: black;
etc.
..
}
>
contentDiv.setA ttribute("class ", "active")

Yeah, be careful doing this though. Imagine you've got:
<div id="contentDiv " class="class1 class2 inactive">bhakj fh</div>

You want to switch between active and inactive and you do:

contentDiv.setA ttribute("class ", "active")

and suddenly it's:

<div id="contentDiv " class="active"> bhakjfh</div>

Whereas what you really want is:

<div id="contentDiv " class="class1 class2 active">bhakjfh </div>

So you probably want to use the split method on contentDiv.clas sName instead
to get an array of class names, then replace inactive with active, glue the
strings in the array back together and reassign it

[Garmt de Vries]

Re: How Does JavaScript Call Forth CSS??

On Apr 27, 6:21 am, "Nik Coughlin" <nrkn....@gmail .comwrote:

Yeah, be careful doing this though.  Imagine you've got:
<div id="contentDiv " class="class1 class2 inactive">bhakj fh</div>
>
You want to switch between active and inactive and you do:
>
contentDiv.setA ttribute("class ", "active")
>
and suddenly it's:
>
<div id="contentDiv " class="active"> bhakjfh</div>
>
Whereas what you really want is:
>
<div id="contentDiv " class="class1 class2 active">bhakjfh </div>
>
So you probably want to use the split method on contentDiv.clas sName instead
to get an array of class names, then replace inactive with active, glue the
strings in the array back together and reassign it

Or do:

function activate_item() {
this.className= this.className. replace(/passive/,'active'); // change
passive to active
}

function passivate_item( ){
this.className= this.className. replace(/active/,'passive'); // change
active to passive
}

[Evertjan.]

Re: How Does JavaScript Call Forth CSS??

Garmt de Vries wrote on 27 apr 2008 in comp.lang.javas cript:

Or do:
>
function activate_item() {
this.className= this.className. replace(/passive/,'active'); // change
passive to active
>}
>
function passivate_item( ){
this.className= this.className. replace(/active/,'passive'); // change
active to passive
>}
>

Perhaps:

function toggle_item(){
this.className=
(/active/.test(this.clas sName))
? this.className. replace(/active/,'passive')
: this.className. replace(/passive/,'active');
};

--
Evertjan.
The Netherlands.
(Please change the x'es to dots in my emailaddress)

[david.karr]

Re: How Does JavaScript Call Forth CSS??

On Apr 27, 4:21 am, "Nik Coughlin" <nrkn....@gmail .comwrote:

Ben C wrote:

On 2008-04-27, Nik Coughlin <nrkn....@gmail .comwrote:

"Prisoner at War" <prisoner_at_.. .@yahoo.comwrot e in message
>news:c86208c 9-45fb-4419-acb6-6d62c94d4ef0@m4 4g2000hsc.googl egroups.com...

>

>Okay, Folks,

>

>I guess my real burning concern all along is a "high-level" one:
>just how does JavaScript interact with CSS?

[...]

Basically, you get the element in Javascript, and set its style
property.

>

<div id="content">bl ah</div>

>

JavaScript:

>

var contentDiv = document.getEle mentById( "content" );
contentDiv.styl e.marginLeft = "1em";

>

Generally (there may be exceptions but I'm not aware of any) the
property of the object corresponds to the name of the CSS property
but camel cased.

>

Yes. Another way to do it is to change the class attributes of
elements with setAttribute.

>

Then you can organize the styles in style sheets rather than packing
them all into the elements' style attributes, and just switch the
elements' classes so they get selected by different selectors.

>

This kind of thing:

>

.active
{
border: 2px solid red;
background-color: yellow;
color: black;
etc.
..
}

>

contentDiv.setA ttribute("class ", "active")

>
Yeah, be careful doing this though. Imagine you've got:
<div id="contentDiv " class="class1 class2 inactive">bhakj fh</div>
>
You want to switch between active and inactive and you do:
>
contentDiv.setA ttribute("class ", "active")
>
and suddenly it's:
>
<div id="contentDiv " class="active"> bhakjfh</div>
>
Whereas what you really want is:
>
<div id="contentDiv " class="class1 class2 active">bhakjfh </div>
>
So you probably want to use the split method on contentDiv.clas sName instead
to get an array of class names, then replace inactive with active, glue the
strings in the array back together and reassign it

It's probably best to use reusable code for operations like this, and
fortunately all of the major JS frameworks include this. The
following URL provides a good summary of this:

http://www.openjs.com/scripts/dom/class_manipulation.php

[Joshua Cranmer]

Re: How Does JavaScript Call Forth CSS??

Prisoner at War wrote:

Okay, Folks,
>
I guess my real burning concern all along is a "high-level" one: just
how does JavaScript interact with CSS?

Depends on what level of "interactio n" you're specifying. Direct
manipulation of style rules is handled by something called the `CSS
Object Model' (still a WIP, IIRC); but computed style rules can be
affected by DOM mutations. It is the latter that is more often the case.

Right now, my newbie self only knows JavaScript and CSS to *co-
exist*...but I'm beginning to get the sense that they actually
interact -- or, perhaps more precisely, JavaScript acts upon CSS...but
how, exactly??
>
I see how JavaScript acts upon HTML, but I'm not so sure where
JavaScript acts upon CSS...moreover, I want to see where they could
create whole new browsing experiences, beyond simply new text and new
images (though I'm only just beginning at the level of new ways of
presenting text and images)....

In short, most JavaScript tends to act on CSS only by proxy through the
HTML. In my code, I generally modify styles by changing the classes of
elements.

P.S. The `DOM', or `Document Object Model', is the precise specification
that most people think of when the think of JavaScript; any time you're
dynamically modify DOM (e.g. through document.getEle mentByID), you're
actually using the DOM. Most literature tends to gloss over this
distinction.

--
Beware of bugs in the above code; I have only proved it correct, not
tried it. -- Donald E. Knuth

[Harlan Messinger]

Re: How Does JavaScript Call Forth CSS??

Garmt de Vries wrote:

On Apr 27, 6:21 am, "Nik Coughlin" <nrkn....@gmail .comwrote:

>Yeah, be careful doing this though. Imagine you've got:
><div id="contentDiv " class="class1 class2 inactive">bhakj fh</div>
>>
>You want to switch between active and inactive and you do:
>>
>contentDiv.set Attribute("clas s", "active")
>>
>and suddenly it's:
>>
><div id="contentDiv " class="active"> bhakjfh</div>
>>
>Whereas what you really want is:
>>
><div id="contentDiv " class="class1 class2 active">bhakjfh </div>
>>
>So you probably want to use the split method on contentDiv.clas sName instead
>to get an array of class names, then replace inactive with active, glue the
>strings in the array back together and reassign it

>
Or do:
>
function activate_item() {
this.className= this.className. replace(/passive/,'active'); // change
passive to active
}
>
function passivate_item( ){
this.className= this.className. replace(/active/,'passive'); // change
active to passive
}

While easier to program, the downside to this as a general approach is
that you can wind up changing things you didn't mean to change.

class="one alone"

Replace class "one" with class "two":

class="two altwo"

which is probably not what was intended.

[Nik Coughlin]

Re: How Does JavaScript Call Forth CSS??

"Harlan Messinger" <hmessinger.rem ovethis@comcast .netwrote in message
news:67osepF2q5 5i5U2@mid.indiv idual.net...

>Or do:
>>
>function activate_item() {
> this.className= this.className. replace(/passive/,'active'); // change
>passive to active
>}
>>
>function passivate_item( ){
> this.className= this.className. replace(/active/,'passive'); // change
>active to passive
>}

>
While easier to program, the downside to this as a general approach is
that you can wind up changing things you didn't mean to change.
>
class="one alone"
>
Replace class "one" with class "two":
>
class="two altwo"
>
which is probably not what was intended.

Yep but you can match regular expressions against whole words only which
would avoid that issue

[dhtml]

Re: How Does JavaScript Call Forth CSS??

On Apr 29, 3:36 pm, "Nik Coughlin" <nrkn....@gmail .comwrote:

"Harlan Messinger" <hmessinger.rem ovet...@comcast .netwrote in message
>
news:67osepF2q5 5i5U2@mid.indiv idual.net...
>
>
>

Or do:

>

function activate_item() {
this.className= this.className. replace(/passive/,'active'); // change
passive to active
}

>

function passivate_item( ){
this.className= this.className. replace(/active/,'passive'); // change
active to passive
}

>

While easier to program, the downside to this as a general approach is
that you can wind up changing things you didn't mean to change.

>

class="one alone"

>

Replace class "one" with class "two":

>

class="two altwo"

>

which is probably not what was intended.

>
Yep but you can match regular expressions against whole words only which
would avoid that issue

And that is something that was discussed on DHTML Central about 6
years ago. The first approach is the basic idea, but doesn't work, as
Harlan pointed out.

The pattern "(^|\\s)"+token +"($|\\s)" has been adopted by all the
libraries and further optimized to use non-capturing groups. The
pattern is now: new RegExp("(?:^|\\ s)"+token+"(?:$ |\\s)");

It can be a performance boost to cache the patterns (though only if
the cache is used). YUI seems to have discovered this, too.

Basic idea is that it's faster to get an object from a cache than
create one, even if it means an extra function call.

http://www.dhtmlkitchen.com/learn/js/perf/objects/regexp-cache.html

http://www.dhtmlkitchen.com/ape/build/dom/classname-f.js

Garrett

[Prisoner at War]

Re: How Does JavaScript Call Forth CSS??

On Apr 27, 2:20 pm, "david.karr " <davidmichaelk. ..@gmail.comwro te:

>
>
It's probably best to use reusable code for operations like this, and
fortunately all of the major JS frameworks include this. The
following URL provides a good summary of this:
>
http://www.openjs.com/scripts/dom/cl...nipulation.php

Cool, thanks! I'd actually managed to google up JQuery but I wasn't
sure about JavaScript "libraries" and all that....

[dhtml]

Re: How Does JavaScript Call Forth CSS??

On Apr 30, 6:59 pm, Prisoner at War <prisoner_at_.. .@yahoo.comwrot e:

On Apr 27, 2:20 pm, "david.karr " <davidmichaelk. ..@gmail.comwro te:
>
>
>

It's probably best to use reusable code for operations like this, and
fortunately all of the major JS frameworks include this. The
following URL provides a good summary of this:

>

http://www.openjs.com/scripts/dom/cl...nipulation.php

>

Wow, I guess libraries are still using capturing groups. I thought it
was pretty common knowledge to use non-capturing groups. They've got
that right in the tutorial and I can even see in Prototype JS:

removeClassName : function(elemen t, className) {
if (!(element = $(element))) return;
element.classNa me = element.classNa me.replace(
new RegExp("(^|\\s+ )" + className + "(\\s+|$)") , ' ').strip();
return element;
}

A capturing group stores the whitespace:
(\\s+|$)

A non-capturing group does not:
(?:\\s+|$)

It is less efficient to use a capturing group.
A capturing group increases the count of the backreference number, so
for more complicated expressions, it would be harder to keep track of
which group is which number, e.g. \1 or $1.

It would actually be possible to make the Prototype JS function even
less efficient by adding the batch() functionality of YUI. But I'd
have to day they've done a pretty bad for a major library. The
assignment in the conditional, the extra call to $(), the capturing
regexp (^|\\s+), the misnaming of trim() as "strip()" (and the adding
of this misnamed trim() function to String.prototyp e).

At first guess, it seems that Prototype JS's "strip()" is a
normalize() function, but it's not. It's a trim() function, misnamed.
trim() (or strip()) doesn't wipe out the whitespace in the middle, so
you end up with "foo bar baz quux" -remove "bar" -"foo baz quux" -

remove "baz -"foo quux". The add

It's quite surprising to see such code in such a popular library, at
least to me.

In takinga look at jQuery, i find another algorithm that is even
slower. So I have to take back what I said above about "the only thing
that could make the Prototype JS function slower". I didn't think
about the jQuery approach. Create a method "addClass" that delegates
to className.add, which splits the classname to an array, then uses an
each() function, then inside that function, check to make sure the
nodeType is 1.

Here it is:

http://code.jquery.com/jquery-latest.js

className: {
// internal only, use addClass("class ")
add: function( elem, classNames ) {
jQuery.each((cl assNames || "").split(/\s+/), function(i, className)
{
if ( elem.nodeType == 1 && !jQuery.classNa me.has( elem.className,
className ) )
elem.className += (elem.className ? " " : "") + className;
});
},


The function is intended to be called on a Decorated collection, which
would mean an extra call to each(). In most cases, that could be
replaced by adding a fragment identifier to the css file, and then
adding a class to the ancestor.

..window .link {}

/* adding a class to .window object's changes the links */
..window-raised .link { color: red }

/* jQuery tends to encourage this instead */
..window .link-active { color: red }

Cool, thanks! I'd actually managed to google up JQuery but I wasn't
sure about JavaScript "libraries" and all that....

I'm not so sure about those JavaScript libraries, either.

[Thomas 'PointedEars' Lahn]

Re: How Does JavaScript Call Forth CSS??

dhtml wrote:

On Apr 30, 6:59 pm, Prisoner at War <prisoner_at_.. .@yahoo.comwrot e:

>On Apr 27, 2:20 pm, "david.karr " <davidmichaelk. ..@gmail.comwro te:

>>It's probably best to use reusable code for operations like this, and
>>fortunately all of the major JS frameworks include this. The
>>following URL provides a good summary of this:
>>http://www.openjs.com/scripts/dom/cl...nipulation.php

>
Wow, I guess libraries are still using capturing groups. I thought it
was pretty common knowledge to use non-capturing groups. They've got
that right in the tutorial and I can even see in Prototype JS:

^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^
Therefore, chances are it is a really bad idea to do that. In fact, it
turns out that non-capturing parentheses are not supported before JavaScript
1.5, JScript 5.5, ECMAScript Ed. 3. Use them and your script will break in
IE before version 5.5, for example.

A capturing group stores the whitespace:
(\\s+|$)
>
A non-capturing group does not:
(?:\\s+|$)

True, after a fashion.

It is less efficient to use a capturing group.

Nonsense. The tiny amount of memory saved by not storing the backreference
is bought with the tiny amount of runtime that is required more to parse the
non-capturing expression.


F'up2 cljs

PointedEars
--
Use any version of Microsoft Frontpage to create your site.
(This won't prevent people from viewing your source, but no one
will want to steal it.)
-- from <http://www.vortex-webdesign.com/help/hidesource.htm>