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Div ID Selectors or CSS classes for Layout

I've been using ASP.NET and CSS for Layout for a while now, but am not sure whether to use CSS classes or id selectors as the main means of controlling layout and style. For a while I've used mainly id selectors, but now I see there seems to be a trend towards CSS classes.

I guess the real question is when to use id selectors, and when to use classes. They both have their purposes, but it's easy to fall into using mainly one or the other. Microsoft samples seem to be using mainly classes these days??
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mitdaniels
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mitdaniels
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3 Solutions
 
Dave BaldwinFixer of ProblemsCommented:
'id's are supposed to unique on a page so that javascript can find the one and only instance of that id.  Classes are meant to be more general to be used where ever they are needed or wanted.

http://www.w3schools.com/css/css_id_class.asp
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RouchieCommented:
To build on DaveBaldwin's excellent answer, and give you an example, use ID's on elements that occur once - so - a navigation bar might only appear at the top of the page, so that could have CSS applied via ID.
Another example might be a footer <div> containing copyright message.  It only appears once at the bottom, so ID could be used there too.

However, as you are aware, the above could use a CLASS instead.  It makes no difference really.  When using Javascript to locate elements (e.g. to perform functions on elements using JQuery, e.g. hide/show a footer based on a condition), finding elements by ID values is much faster than by class.  Therefore, by using CSS with ID, developers avoid having ID and CLASS together for certain elements.

Hope that helps.
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mitdanielsAuthor Commented:
Thanks for the comments.

Therefore, by using CSS with ID, developers avoid having ID and CLASS together for certain elements.
Are you saying that we should try not to use ID selectors and classes together for the same DIV or element?
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RouchieCommented:
If you can avoid it, it just makes for easier maintenance and makes the code easier to read and/or debug
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mitdanielsAuthor Commented:
Thanks, just what I needed.
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