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What's the difference between an id and a class?
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Lately I'm working with a lot of Wordpress themes. When I have to edit a particular element, I usually use Firebug to see the element's name so I can change the CSS. I think I understand the difference between IDs and Classes, Classes are used for a group of elements that you want to share the same styling, and ID is usually used for a single element.
Here's the thing, I'm seeing so many elements in these Wordpress themes that are only used once, but they are assigned to a class. A good example is the website logo. Isn't the logo only used once? Shouldn't it be assigned to an ID? Why is it always assigned to a class?
Needs change often. An element/style that today you think will only be used once may be used multiple times in the future. Maybe you will have your logo more than one time on your site (for example, on your about us page). Perhaps you may eventually incorporate a second search bar. There are very few cases where you know with 100% certainty that the style will only be needed once.
Here's a good read on the subject: http://oli.jp/2011/ids/
http://ryanfait.com/articles/the-difference-between-ids-and-classes/
Ryan says
"I take a different stance than most web designers when it comes to
using ID's and classes. The vast majority of CSS coders use ID's for
any elements that are simply used once on a page. However, I only use
classes to style my websites, but, when I want to use an element in
JavaScript, I use an identifier. From a presentational standpoint,
styling elements with classes looks exactly the same as styling them
with ID's, but the flexibility of classes offers a certain appeal even
if I don't plan on using a class more than once on a page. Also, when
I see an ID in my XHTML, it reminds me that there is some JavaScript
that refers to that element. It's up to you, but so long as you
implement classes and ID's properly, it is more or less a matter of
personal choice when to utilize one or the other."
id is a unique one, but when class its not, you can you one for many selectors
ID's are unique
Each element can have only one ID
Each page can have only one element with that ID
Classes are NOT unique
You can use the same class on multiple elements.
You can use multiple classes on the same element.
Any styling information that needs to be applied to multiple objects
on a page should be done with a class. Take for example a page with multiple "widgets":
There are some reasons why people prefer using classes instead of id's in CSS. (note that for javascript ID's are still commonly used).
The class element is re-usable on that page. This means that you won't have as much duplicated code with Classes as you would have with ID's.
Usually, IDs refer to something very specific, and abstracting would be tough
Any performance gains picked up by using id, is negated by adding any other selector to the left fo that id. Which mainly means that in most uses of id's you won't really have performance gains. (you could even have less performance than if you would just use a class)
Lecture about this:
http://screwlewse.com/2010/07/dont-use-id-selectors-in-css/
http://www.impressivewebs.com/css-specificity-irrelevant/
http://www.baldurbjarnason.com/notes/ids-in-css/
If you're new to web development, just use the simple rule:
If you're trying to apply style to a HTML element, use a class.
If you're trying to interact with a HTML element with javascript, use an ID.
You see more of classes because they can be reused and assigned to multiple elements.
However an id can belong to only one element at a time hence less of them.
Classes only appearing once:
Such cases like the one you identified, you may call them semantically incorrect as id is more appropriate choice for that but still it would work and it probably happens couple of times that we get to use class which only appearing once (may be while defining that class we are thinking that we can use it somewhere also but at the end we really dont), beside general habit another reason could be:
That class styling is also used somewhere else along with another class for e.g.:
.logo{
width:250px;
height:250px;
float:left;
}
.logo class is applied to logo <div class='logo'>...</div> But there is another element which also require same three properties of logo and some other also so one can reuse logo there also.
<div class='otherstyle logo'>...</div> this would apply the style of logo as well as otherstyle to it.
In some other words to sum it up. The cardinality of a class is 1...* so you can use it one and more than one time. But for id it is 1...1 you will and only use it only once.
Lots of websites use class names like floatleft, clearfloat, alignright, small, center etc that describe the style that is attached to the class. This seems to make sense so when writing new content you can easily wrap (for example) <div class="clearfloat">...</div> around your element to make it behave the way you want.
My question is, doesn't this style of naming classes go against the idea of separating content from presentation? Putting class="floatleft" on an element is clearly putting presentation information into the HTML document.
Should class names like this that directly describe the attached style be avoided, and if so what alternative is there?
To clarify, this isn't just a question of what to name classes. For example a semantically accurate document might look something like:
<div class="foo">Some info about foo</div>
...
<div class="bar">Info about unrelated topic bar</div>
...
<div class="foobar">Another unrelated topic</div>
Say all these divs need to clear floats, the css would look something like:
div.foo, div.bar, div.foobar {
clear:both;
}
This starts to get ugly as the number of these clearing elements increases - whereas a single class="clearfloat" would serve the same purpose. Is it recommended to group elements based on the attached styles to avoid repetition in the CSS, even if this means presentational information creeps into the HTML?
Update: Thanks for all the answers. The general consensus seems to be to avoid these class names in favour of semantic names, or at least use them sparingly provided they don't hinder maintenance. I think the important thing is that changes in the layout should not require excessive changes to the markup (although a few people said minor changes are okay if it makes overall maintenance easier). Thanks to those who suggested other methods to keep CSS code smaller as well.
It's great until you re-design, and narrow is highlighted yellow, center converts better left-justified, and the image you called floatleft now belongs on the right.
I'll admit to the sin of using floatleft and clear as CSS class names, but it is much easier to maintain your CSS if you choose names that relate to the semantic meaning of the content, like feedback and heroimage.
Presentational class names
The HTML spec is clear on this issue:
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.
Does clearleft describe the nature of the content? Not really. Eric Meyer made a joke about this a while ago.
Try to find a structural relation between the seemingly unrelated elements
Let's say you have paragraphs about ducks, paragraphs about monkeys and paragraphs about frogs. You want them have a blue background.
<p class="duck"></p>
<p class="monkey"></p>
<p class="frog"></p>
You could add this CSS rule:
p.duck, p.monkey, p.frog {
background-color: blue;
}
But aren't they all animals? Just add another animal token:
<p class="animal duck"></p>
<p class="animal monkey"></p>
<p class="animal frog"></p>
And change the CSS rule to:
p.animal {
background-color: blue;
}
It is hard and it might not always be possible but the important thing is not to give up quickly.
What if you can't?
If you have a lot of elements with absolutely no structural relation between them, that indicates a structural problem with your document. Try to decrease these elements. That said, grouping n CSS selectors on one rule is still better than adding n presentational class tokens in your HTML document.
Style classes should be semantic. This is a great article on semantic web page design (well, I found it really helpful anyway).
EDIT: I just read another article that makes some good points for using things like display: inline-block, display: table etc. instead of floats. That should help avoid those pesky floatleft and clearfix classes. Making them semantic is always up to you though.
The main problem with having classes named floatleft, clear or the like is the fact that changes in the design imply changes in the HTML markup. This should not happen, true separation between content and presentation is achieved only when you can re-use the same markup in multiple designs or even media (think sharing the same HTML between desktop and mobile versions of your site and only switching sylesheets).
Now, for a practical example :). To add on Fredrik's answer, LESSCSS allow you to hide styles declarations/mixins from developers. This way you can protect reusable components in your stylesheets without the danger of having them pop up in your HTML.
Sample markup:
<div class="branding">Company Name</div>
Sample less code:
// example of reusable functions
.noText() {
color: transparent;
text-indent: -9999px;
}
.clear-after() {
&:after {
content: ".";
display: block;
visibility: hidden;
height: 0;
clear: both;
}
}
.branding {
.clear-after();
.noText();
background-image: ...;
}
Of course, for mobile you might just want to have the company name in bold, without any other styling:
.branding {
color: pink;
font-weight: bold;
}
I think it depends on how you are using the styles.
Content should be named accordingly, as the style may change but the content will likely remain the same.
For instance, if you have a div that contains stock info, you should name the div something like div class="stockInfo", so that no matter what the presentation, you can change the styles and the name will not contradict those styles (as opposed to naming the div div class="yellow" and then changing the background-color to red).
However you will have "helper styles" and these should be named for what they do.
For instance, you will likely want to use a <br /> to clear some floats. In this case, it is perfectly reasonable to name it <br class="clear" /> and to give it a style of br {clear:both;}.
Again, most Web sites float their images right or left. To assist with this, you can set <img class="right" src="" /> and <img class="left" src="" /> and then have the styles to match, img.right {float:right;} etc.
So it depends on the usage.
Class names and ids that describe the function is better than using names that describe the styling of the element.
I usually end up not doing it religiously though, because it is in my opinion more convenient to i.e. clear floating elements by using the famous clearfix hack rather than adding clear:both all over the stylesheets.
But I think that LESS and SASS creates interesting opportunities to get the best out of both worlds, because you can have mixins and functions that describes some style and still have semantic correct names by just including whatever 'style' you want.
Instead of having this HTML and CSS
<div class="navigation roundedcorners">...</div>
.roundedcorners {
-moz-border-radius: 5px;
-webkit-border-radius: 5px;
border-radius: 5px;
}
you could use SASS to create this mixin:
=rounded-corners
-moz-border-radius: 5px
-webkit-border-radius: 5px
border-radius: 5px
and include it into your .navigation class like this:
.navigation
+rounded-corners-5px
which would reduce your HTML to this:
<div class="navigation">...</div>
and therefore still get the advantage of having semantic correct names while having a convenient way to share styles between different elements.
Andrew; it's good to give sensible name to an class & id which easy to understand for you & your fellow member's which are working on that project. For me classes small , center , floatleft etc define nothing to me because when you give class center that's indicate that the element on the center but there are other properties also in that class like color, background etc
For example
<div class="wrap">
<div class="center">lorem</div>
</div>
css:
.center{margin:0 auto;}
in this example class center don't clear to me. but we can use them as a helper class.
For example
<div class="wrap">
<div class="panel center narrow">lorem</div>
</div>
css:
.center{margin:0 auto;}
from above example now it clear to me what the role of class center in that panel div
FOR MORE CHECK THESE LINKS :
What's the best way to name IDs and classes in CSS and HTML?
http://www.ronniesan.com/blog/entry.php?title=organizing-your-dom-elements-with-the-proper-ids
http://cssglobe.com/post/3745/my-top-10-most-used-css-class-names
If your question is:
Is it recommended to group elements
based on the attached styles to avoid
repetition in the CSS, even if this
means presentational information
creeps into the HTML?
Then my flat answer would be that in real world, semantic and presentation isn't everything. So my answer would be: it depends.
...depends if bandwidth is important to you... On a site with many visitors per hour, then the classnames could even simply be something like "c11" (yes, I've seen it) instead of meaningful, but looong class names.
...depends also if you perfectly know that when the look and feel will change, then the CODE will change also. (exemple: you redesign a site today in XHTML, but you perfectly know that when you'll re-do the CSS in 2 years, then you'll want the markup to be HTML5, so you will pretty much change the structure anyways...)
...depends also if you're already 3 days late on a delivery. When you're 3 days late, believe me, classnames like "nopadding" starts to appear, as you don't have anymore time to think straight about semantic (neither does your client).
Depends on so many things, I'd say... That's my "real life" point of view of your question.
From what I've seen, developers have the tendency to overload their HTML pages with way too many unnecessary classes and extra markup. These classes not only make the page size bigger (and thus the load time longer), they also crowd up the page and make it difficult to manage and modify at a later time.
Having things like center and float-left might be helpful when you're dealing with display text that was input by a user (such as a post on a forum), but for general markup purposes you're better off just adding text-align: center and float: left to the appropriate classes. This especially helps if you are trying to change the appearance of your site without changing the HTML much. The less you have hardcoded into your template, the easier it is to only have to change around the CSS when modifying your template. That bit alone is worth it to me.
As a general rule of thumb, you really should only give elements classes when it describes what the content is, not where or how it is being displayed. i.e. <span class="movie-information"> instead of <span class="bold">.
The only time I feel that it makes sense to give an element a class when it isn't necessary is if you are concerned with Search Engine Optimization. You should definitely read up on Microformats if you are interested in seeing how adding the right classes can actually help search engines. That being said, adding classes that describe how the page is visually displayed does nothing for the search engines.
The only time I would ever "group" classes is if they are either displaying the same thing, or if they are siblings. It gets really messy in your CSS when you have elements from all over your page defined together. You're much better off grouping your classes in your stylesheet in ways that you will be able to find them later, rather than saving a few lines by combining them.
I think this is where old meets new in web technologies. From times past, it has been difficult to unobtrusively render an outstanding web experience. These class names mostly came in handy when websites were changing webmasters to aid them in understanding the code. It served its cause well but with the new technologies of this day and age, I think this is slowly dying out - infact, it should be dead.
The question we should ask is, "Do we need to create a new class for every new innovative design that could pass as a template?". I do not think so. The markup on a site should do what it is meant for - markup. The class names used in the markup should be descriptive of the content and not its looks. The stylesheets - on the other hand - should be able to select elements on a document based on the information in the markup, and style them.
I want to relate this to the Rails association naming convention. Consider this...
class Post < ActiveRecord::Base
has_one :personifyable
has_many :personifications, :through => :personifyable
has_many :taggables
has_many :tags, :through => taggables
belongs_to :destroyers
end
Obviously, this is not a real model; it is something I am using to drive a point. Consider the case of a deeply nested dependency. These names will grow ridiculous - if they aren't already (i.e. in CSS, <div class='mediumwidth floatright centeredtext graytheme master'></div> or something of the like)
Now consider the case where you have different principles. Different developers and designers may - if not 'most definitely will' - have different reasons for using a specific naming convention. How would this affect refactoring time. I will leave that to your imagination. Also, if your business partner notices a new trend with sites themes that attracts traffic - more technically, assume this business partner has performed some experimental A/B testing and come up with some specs - you don't want to change the contents of the whole stack (ie HTML and CSS and possibly JS pages) to implement this new style.
In conclusion, keep styling hints out of your markup. Unobtrusively interact with the document to style and manipulate it. Sass gives you a fine way of styling a site while having your CSS mock your markup. jQuery is another awesome UJS library. HTML5 gives you methods too that make the markup more flexible and yields more information to CSS and JS.
I don't think adding a descriptive class name to your document is really a big issue. I find it's easier to work with explicit class names like "floatleft" as opposed to things that are purely semantic or reliant on the cascade. It's usually easier for later developers who don't have the document structure in their heads as well.
You don't want to use them for everything--you wouldn't want to add a class of floatleft to every li in a left-floated menu, but these kind of styles are very good when you need to do a specific thing to one or more elements, and you want to make other developers aware that you did it.
It's like putting in <div class="clear"> or even <div style="clear:both;">: maybe not the prettiest but it sure is obvious what you are doing.
My rule of thumb is: whatever makes you have to think less, do that.
EDIT: As I said in my comment above, this is most true for classes that refer to clearing and floats, i.e., things that are purely presentational, non-semantic, and yet must be referred to in the HTML. I think in this case it is actually preferable to indicate that you are using a purely presentational class, like floatleft, rather than forcing the float to be attached to some semantic element.
I am a developer before a programmer, so for me I use something like a "floatleft" css class as a sort of UtilityMethod.
Meaning, my css class is "floatleft"...and that's all that class does.
so if I say <div class="floatleft"></div> in my mind that is saying "make this div float to the left".
So if that Div also needs a blue background and is my main header it's going to have a different class for that and I end up with <div class="mainheader floatleft"></div>
Doing it this way also avoids issues with refactoring. If I am changing my design later, I will know that "floatleft" ALWAYS floats things left and nothing more.
I think, at the end of the day it is about what works for you. If your class name is descriptive of what it does, that does not really go against the rule of separating markup from styles. Another factor to consider is, are you the sole developer, or part of a team. If you are part of a team, or you know your code will be worked on later by other devs, you should establish, and document the naming conventions used.
I am currently contracting with Down Jones on some very large projects, and we have a rather lengthy document on naming conventions for our classes, including when to use camel-case, or dashes or underscores, as well as specific prefixes on the class name based on the project we work on. It sounds crazy, but when you have a dozen or so front-end devs working on stuff at the same time, it is a life saver!
You are saying something like this:
.red
{
color:red;
}
so in order to use this class:
<ul>
<li class="red">hello</li>
</li>
ALTERNATIVE SOLUTION
ul li
{
color:red;
}
Usage:
<ul>
<li>Hello</li>
</ul>
By this you can actually remove the presentation information from the content.
I personally name them things close to what they will be doing. Say I have a class that is on an image gallery and its a primary most used class it will be something like "gallery" or if I'm setting borders around things that are meant to be more decorative I'll name it "decoborder". I try to keep them semi short and somewhat related what task they provide. I don't like to do things like "small, large, H1underlined" or anything that can mimick another tag or function because that can just get confusing. Beyond that I think you should really name it in whatever way makes the most sense to you.
If the question is only one of naming, then for one specific class...
class="floatleft"
or
class="myClass"
or
class="gibberish"
....changes absolutely nothing. They are only different class names. The programming functions the same.
Either your content & presentation is separated, or it isn't... totally regardless of how you created the names.
For what it's worth, if I remember correctly the class keyword in HTML isn't currently used for anything other than CSS stylesheets. Thus, the example that you provided...
<div class="foo">Some info about foo</div>
...
<div class="bar">Info about unrelated topic bar</div>
...wouldn't really be a way of identifying data. I would suggest either the name or id attribute if you really want to identify data within your HTML tags. (They both have slightly different uses - name is generally used for server-side queries while id can be styled and is generally more versatile. IDs must be unique, but names don't have to be.) You can check further documentation using the W3C HTML specification.
In short - don't worry about tying content to presentation through your tag classes; until they're specifically used for anything else, they will not have any real effect on your raw content. As such, I'd say name your classes whatever you want, as long as it makes sense. Personally, I would err on the side of logical naming versus style-type naming (e.g. class name "editorcomment" instead of class "graybgfloatleft" or something like that), but in the end, your class names aren't going to tie your data to your presentation like an ID or a name would.
Good luck.
I've done both and I have to say nowdays I lean towards using non presentational classnames. I found this nifty framework called OOCSS https://github.com/stubbornella/oocss/wiki which helped me alot when I was creating a new layout for my web application and suited my requirements so well.
It is mostly because the definition of basic classes for spacing, headers and text works so well when you have to deal with alot of content. Because you use the same classes everywhere it helps make the layout better and maintainable.
Offcourse this means a element in your html can look like this: <div class="unit size1of3 lastUnit"> But isnt that what HTML is about? Making sure your information is presented properly.
I disagree on the whole redesign point, be honest, when you have to redesign your website most CSS goes out the door anyways. And, by dividing the CSS into proper classes for spacing/heading/text it becomes less likely to have conflicting css rules that mess stuff up like ul li div{}
Offcourse the classes do not describe the contents, but as CSS does not allow class inheritance and you have to support old technology like IE6...does it really matter? And do classnames like animal and duck really make for better html? Id like to think HTML is for the browser and when the browser renders it, thats for humans.
It depends, sometimes it makes sense just to add a class to let an element float. The problem with the semantic approach is that you will end up ball of mud of css classes. Sure, names like redLink or blackHeader have to be banned but sometimes you will need little helpers like "clear" or "floatLeft".
Read this article of Nicole Sullivan who explain this in deep.
There are two things that I feel get entirely left out of these discussions all too often. The first is WHY you would want to be all semantic or all not. The keywords are Branding and Skinning. Presentational class names may be justifiable if you work on some internal, departmental websites where branding and skinning will never in a million years get funding. On the other hand, customer facing sites, such as car manufacturers and department stores live in a world where every single new product that gets launched results in an entirely new skin for the website. New colors, new layout, new background images and all of this lead by designers who should be able to make the change purely in css so there's no chance they can break any working php (or what-have-you). There are also branded sites, where you have multiple skins, potentially running on the same site simultaneously. On sites with that requirement, you can't have visual changes impact html or you end up breaking every other brand just to update one of them. In these situations, semantic class names are a necessity.
The second thing that often gets left out is how to combat the problem of repeating groups of properties created by semantic class names, as in:
.content-nav {
float: left;
margin-right: 10px;
background-color: #ccc;
}
.content-nav .user-photo {
float: left;
margin-right: 10px;
border: solid 1px #000;
}
.content-nav .user-display-name {
float: left;
margin-right: 10px;
text-decoration: underline;
}
People often point this out as a drawback of semantic names, and I think that that's a valid point. On the other hand I would like to point out that there are tools that can help you keep semantic css DRY, such as LESS and SASS. I did see one other commenter mention this above, but I just thought that this point was worth highlighting.
I am a web developer for almost 2 years now and I am still learning new things every day, but since my knowledge gets bigger, I came across some fundamental question and couldnt find a good discussion about it.
How do you name your DIVs, IDs, Classes? Do you give them specific content related names? (i.e. <div id="google_map">)
Or do you name them related to their position on the site? (i.e. <div id="content_top_bar">)
And do you do this in your .css the same way?
I hope you get what i am trying to find out. I guess there is no "true" answer anyways, but I would like to know some opinions, so that I can decide what option to take and keep working with it in the future.
HTML should be used as semantically as possible, so your classes and IDs should be named for their content, not for their style, or their position within the site (these things should be able to change without effecting your HTML.
For example, if you name a <div id="left-sidebar"> and then later decide you'd like to move that element, the id no longer would semantically represent the element. Conversely, if you named a <div id="navigation"> or <div id="article"> they would still represent the element, regardless of their placement or styling on the page.
I would name objects based on their content (whether logical of physical). You care what an object is not where it's at.
The exception to the above rule is when the object forms the layout of the page, but in that case it shouldn't really have a name anyway, unless you intend to manipulate the structure of the page to move stuff around at run-time (which is fine, just rare).
Also I find myself not naming a lot of objects anyway, but assigning them classes, especially for related objects that I have to manipulate together. It makes working with them through jQuery (or whatever framework you choose) a lot easier.
I think there is a definite answer to this question: Whatever works best for you :)
Some things to consider:
Are you the only one writing in the codefiles or not?
What's the structure of your site and is it static or dynamic?
Depending on these you may opt to choose english names or your own language, or you may opt to name a div "content" rather than for instance "div_homepage".
Hope that was helpful :)
Since HTML is for content, your naming should refer to content.
Depending on what the html element represents:
The element is part of the layout, name it to something that represents that part of the layout.
example: 'footer_top_bar'
The element is used for specific content, name it to something that represents the content.
example: 'comment', 'navigation', 'breadcrumbs'.
I can imagine it can get complicated fast trying to debug style issues when there are multiple classes associated with elements. Currently I'm using multiple classes but in a way that one type of class is for jQuery manipulation and the other is for style. So I can have an element
<div id='myDiv' class'ActionControl SearchBox'></div>
where the .ActionControl is used by jQuery and the .SearchBox has a style associated in the CSS file. Is this right or wrong? What do people more experienced with this think?
What issues have other people come up against? How have they been resolved?
As long as your code is comprehensible, maintainable and clear to others, your system is good.
There is no standard I am aware of in how to give CSS classes, except one:
If you need to target a single element in the page using JS or CSS you should use an ID and not CLASS.
This is definitely a good practice...
What you have to keep in mind always is not to remove the class attribute, instead you will be removing the classes you exactly want to remove.
Also, another problem (not for me) is that multiple classes are not supported for OLDER browsers.
Keep in mind to code your CSS in a way it prevent code duplication so a float:left class can be used in many different elements, this is to keep code clear.
I can't see anything wrong with that. Probably, you could prefix the jQuery classes with e.g. jActionControl, so you have a better overview over who uses what classe if it gets really ugly with many classes.
Of course, you can assign as many classes as you want so there is nothing wrong with your approach in my eyes.
Another way to use multiple classes is to get a kind of inheritance.
.thing { ..blah.. }
.thing.subthing { ..tweaks.. }
<div class="thing"></div>
<div class="thing"></div>
<div class="thing subthing"></div>
Here all the things get "blah" applied to them, but only the subthing div gets the tweaks.
Yes, it can get complicated. As with any power tool, you need to apply it judiciously and with discipline.