considering I have a single css file for my entire website (and that doing so is an usual technique), I was wondering if there is a way to select website-wide attributes like body (or any other attribute in fact) according to the current page using only css.
Something like
body:in('index.html') {
some properties;
}
body:in('contact.html') {
other properties;
}
Again, css only. I know the simple solutions using things like php, js, jquery...
Selectors have no information about the document beyond what is presented in the DOM tree, and the DOM does not expose information about the page according to its file name, URL, or any other such properties.
Historically there was a #document at-rule for querying the current URL, but it was removed from the Conditional Rules Level 3 module. The most likely reason for this is the lack of cross-vendor implementations, as the only known implementation exists in Gecko, as #-moz-document. It's so bad, that the only uses for it that you'll spot in the wild are not to apply CSS based on a certain page, but solely as a CSS hack for Firefox.
As you've stated, the simplest workaround for this is to have each page apply a unique class to the html or body element and select according to that class, whether via hardcoding, or dynamically.
you could add and id atribute to the body tag and style things inside it using:
body#contact div{
background:#376;
color:#857;
/*etc*/
}
more information about selectors in http://www.w3.org/TR/css3-selectors/
I have a GWT code that creates a list (grid as result) and I set the style to a CSS class like
.test tr {
height: 26px;
}
now...if from code I need to obtain that "26px" when the render isn't completed or when the grid has no element? ho can I obtain that value? I know i can do
obj.getElement().getStyle().getProperty("height");
to obtain some style attribute but how can I obtain the sub-element tr related value?
As you've discovered, the element's style property only contains styles that are directly set on the element itself - it does not automatically pick up css that has applied to it, or css that has been applied to parent nodes and inherited to it, etc.
To do this, you need to get the 'computed' style of the element. This is a somewhat expensive operation so should be done carefully, and will not work in older versions of IE, so different code entirely must be written. Some libraries like GXT have a built-in feature to do this work for you (XElement.getComputedStyle(...)), if you are not using a library like that, you will need to write JSNI that can call into this api and ask for these details.
Check out http://caniuse.com/#feat=getcomputedstyle (IE8 and below do not have it, old Android Browser and Opera Mini apparently have issues), and https://developer.mozilla.org/en-US/docs/Web/API/Window.getComputedStyle for the details on the call. In your JSNI, remember to use $wnd to refer to the window object, something like this:
$wnd.getComputedStyle(element).getPropertyValue('height');
There is no need to get that value programmatically. I imagine that you have only one or two styles that define your tables, so you can always infer the row height from your style name. For example, if you have "standard" height set at 26px and have a "big-table" style setting it at 36px, you can simply:
int rowHeight = myTable.getStyleName().contains("big-table") ? 36 : 26;
I have a table where I show/hide a full column by jQuery via a CSS class that doesn't exist:
<table>
<thead>
<tr>
<th></th>
<th class="target"></th>
<th></th>
</tr>
</thead>
<tbody>
<tr>
<td></td>
<td class="target"></td>
<td></td>
</tr>
<tr>
<td></td>
<td class="target"></td>
<td></td>
</tr>
</tbody>
</table>
With this DOM I can do this in one line via jQuery: $('.target').css('display','none');
This works perfectly, but is it valid to use CSS classes that aren't defined? Should I create an empty class for it?
<style>.target{}</style>
Are there any side effects or is there a better way to do this?
"CSS class" is a misnomer; class is an attribute (or a property, in terms of scripting) that you assign to HTML elements. In other words, you declare classes in HTML, not CSS, so in your case the "target" class does in fact exist on those specific elements, and your markup is perfectly valid as it is.
This doesn't necessarily mean that you need to have a class declared in the HTML before you can use it in CSS either. See ruakh's comment. Whether or not a selector is valid depends entirely on the selector syntax, and CSS has its own set of rules for handling parsing errors, none of which concern the markup at all. Essentially, this means HTML and CSS are completely independent of each other in the validity aspect.1
Once you understand that, it becomes clear that there is no side effect of not defining a .target rule in your stylesheet.2 When you assign classes to your elements, you can reference those elements by those classes either in a stylesheet, or a script, or both. Neither has a dependency on the other. Instead, they both refer to the markup (or, more precisely, its DOM representation). This principle applies even if you're using JavaScript to apply styles, as you're doing in your jQuery one-liner.
When you write a CSS rule with a class selector, all you're saying is "I want to apply styles to elements that belong to this class." Similarly, when you write a script to retrieve elements by a certain class name, you're saying "I want to do things with elements that belong to this class." Whether or not there are elements that belong to the class in question is a separate issue altogether.
1 This is also why a CSS ID selector matches all elements with the given ID regardless of whether the ID appears exactly once, or multiple times (resulting in a non-conforming HTML document).
2 The only situation I'm aware of where an empty CSS rule like that is necessary is when some browsers refuse to apply certain other rules properly as the result of a bug; creating an empty rule will cause those other rules to be applied for some reason. See this answer for an example of such a bug. However this is on the CSS side and therefore should have nothing to do with the markup.
There are no ill effects to use classes which don't have styles. Indeed, that's part of the usefulness of CSS is that it's de-coupled from the markup and can style or not style elements/classes/etc. as needed.
Don't think of them as "CSS classes." Think of them as "classes" which CSS happens to also use if it needs to.
According to HTML5 specification:
A class attribute must have a value that is a set of space-separated
tokens representing the various classes that the element belongs to.
... There are no additional restrictions on the tokens authors can use in
the class attribute, but authors are encouraged to use values that
describe the nature of the content, rather than values that describe
the desired presentation of the content.
Also, in the version 4:
The class attribute has several roles in HTML:
As a style sheet selector (when an author wishes to assign style
information to a set of elements).
For general purpose processing by
user agents.
Your use case falls under the second scenario, which makes it a legitimate example of using a class attribute.
You can use a class which has no styles, this is entirely valid HTML.
A class referenced in a CSS file is not a definition of a class, it is used as a selector rule for styling purposes.
When you use a classname in JavaScript, it does not look at the CSS to find that class. It looks directly in the HTML code.
All that is required is that the classname is in the HTML. It does not need to be in the CSS.
In fact, many people think it's actually a good idea to keep separate classes use with CSS and Javascript, as it allows your designers and coders to work independently without getting in each other's way by using each other's classes.
(note, the above paragraph is obviously more applicable for larger projects, so don't feel that you have to go to this extreme if you're working on your own; I mentioned it to make the point that the two can be entirely separate)
You can use CSS classes without using it, but I suggest that if you are adding CSS classes just for the JavaScript/jQuery code, prefix with it js-YourClassName so the front-end developers never use these classes to style the elements. They should understand that these classes can be removed at any time.
The moment you add the Class in your HTML the Class will be defined, so your solution is completely fine
It's not necessary to define CSS classes in your stylesheet. It should work just fine. However, adding it won't harm.
One thing that nobody here has fully mentioned is that JavaScript (aided by jQuery in this case) isn't able to directly modify a document's cascading style sheet. jQuery's css() method merely changes the matched set of elements' style property. CSS and JavaScript are completely unrelated in this aspect.
$('.target').css('display','none'); doesn't change your .target { } CSS declaration at all. What has happened here instead is that any element with a class of "target" now looks something like this:
<element class="target" style="display:none;"></element>
Are there any side effects caused by not pre-defining a CSS style rule? None whatsoever.
Is there a better way to do this? Performance-wise, yes there is!
How can the performance be improved?
Rather than directly modifying the style of each element, instead you can pre-define a new class and add that to your matched elements using addClass() (another jQuery method).
Based on this pre-existing JSPerf which compares css() with addClass(), we can see that addClass() is actually much faster:
How can we implement this ourselves?
Firstly we can add in our new CSS declaration:
.hidden {
display: none;
}
Your HTML would remain the same, this pre-defined class is simply in place for later use.
We can now modify the JavaScript to use addClass() instead:
$('.target').addClass('hidden');
When running this code, rather than directly modifying the style property of each of your matched "target" elements, this new class will now have been added:
<element class="target hidden"></element>
With the new "hidden" class, this element will inherit the styling declared in your CSS and your element will be set to no longer display.
As is mentioned by so many others, yes, using classes with no assigned CSS is perfectly valid and rather than thinking of them as 'CSS classes' you should simply recognise the semantics of class and ID to be groups and individual elements respectively.
I wanted to chip in as I felt an important point hasn't been raised given the example. If you ever need to do visual manipulations to a variable length of elements (in this case you're using table rows) then it always makes sense to recognise that the cost of doing so through Javascript could potentially be very expensive (e.g if you have thousands of rows).
In this situation let's say we know that column 2 always has the potential to be hidden (it's a conscious function of your table) then it makes sense to design a CSS style to handle this use case.
table.target-hidden .target { display: none; }
Then rather than using JS to traverse through the DOM finding N elements we simply need to toggle a class on one (our table).
$("table").addClass("target-hidden")
By assigning the table an ID this would be even quicker and you could even just refer to the column by using the :nth-child selector which would reduce your markup further but I can't comment on efficiency. Another reason for doing this is that I hate inline styling, and will go to great lengths to eradicate it!
It will have no effect if you apply a class on a HTML element, and that class is not defined in CSS. It is a common practice and like Aamir afridi said if you are using classes for js only purpose, it is a good practice to prefix them with js- .
It is not only valid for calsses, but also for id attribute of html elements.
There's no problem at all of using classes to just query for elements. I used to give such class names the sys- prefix (for example, I'll name your class sys-target) to distinguish them from classes used for styling. This was a convention used by some microsoft developers in the past. I also noticed a growing practice of using the js- prefix for this purpose.
If you are not comfortable with using classes for purposes other than styling, I recommend using the Role.js jQuery plugin which allows you to achieve the same purpose using the role attribute, so, you may write your markup as <td role="target"> and query for it using $("#target"). The project page has good description and examples. I use this plugin for big projects because I really like keeping classes for styling purposes only.
Refer to the jQuery validation engine. Even in there we also use non-existent classes to add validation rules on the HTML attributes. So there is nothing wrong in using classes that are not actually declared in a stylesheet.
How is the all property used in CSS?
This question is related to this one.
According to this:
The ‘all’ property is a shorthand that resets all CSS properties.
Name: all
Value: initial | inherit | default
Initial: See individual properties
Applies to: See individual properties
Inherited: See individual properties
Percentages: See individual properties
Media: See individual properties
Computed value: See individual properties
Animatable: See individual properties
So, it has to reset CSS properties for a selector.
This means, for example, that if we import Twitter Bootstrap and add the style below, the .btn class has to be reseted:
.btn {
all: default;
}
This doesn't happen. See this jsFiddle.
Am I correct? Isn't this implemented in web browsers?
The W3C specification you linked to says it's currently in "Working Draft" stage. Also, there's no mention of the all property on CanIUse.com, so I think it's safe to say it's experimental.
You might want to try -webkit-all or -moz-all.
Y'know, reading the spec for this feature, it feels like a hack. If you design your style cascade appropriately there shouldn't be a need for this property.
Right now I believe only Firefox supports all (as of version 27). You can use the all property (e.g. all: unset;) to apply the value to every property (except direction and unicode-bidi).
See this pen in latest FireFox: http://codepen.io/tomliv/pen/AejFH
There are 3 inputs in the grey area (really!).
This is not what I was expecting, but maybe setting all to initial will be more what you need?
There really is no default value for every property - at least one that is consistent across all browsers.
That's really where a CSS reset comes in. I'd recommend looking at Eric Meyer's CSS reset: http://meyerweb.com/eric/tools/css/reset/. Typically, these types of resets are used to reduce browser inconsistencies.
If you're looking to apply something to all elements (you'll still need to individually list each property), use
* { /* Universal Selector */ }
Using a reset stylesheet or some CSS framework like bootstrap is probably a better solution for both normalizing your CSS and cross browser consistency.
I want to know what things can be done "ONLY" with CSS , that are not available using dynamically updated style "attributes" using Javascript. So far I know:
Media queries
Pseudo tags
Any more?
Update:
This question was closed but I asked it as I am trying to decide on the technology to use for a project, but one of the options cannot use CSS style sheets, and can only manipulate the style attribute using javascript.
Inline style attributes can only contain property declarations (e.g. width: 10px or color: red). They can't contain any other CSS constructs: not selectors, at-rules (e.g. #import, #media, #font-face), etc. Just property declarations.
However, they play a big role in the cascade: any styles for an element with that attribute take highest precedence (after considering !important of course).
There's actually an entire module devoted to style attributes, by the way, but it's not essential reading for authors.
So, anything that isn't a CSS declaration, is only possible in a stylesheet, not a style attribute. Not sure if that's what you're asking...
Note that media queries and #media rules are not the same thing; media queries can exist in areas outside of stylesheets too, like HTML's media attribute, where they're next most commonly found.
I believe pseudo classes (:hover etc..) and pseudo elements (:after, :before) cannot be added/manipulated via JS (via the style property i mean) because they are not part of the DOM.