Best practice to including sidebar on some pages, but not all?

[eluser]ELRafael[/eluser]
what i do in my projects:
use js to check if there is sidebar content. in jquery, something like this

Code:

var has_sidebar = $('div.sidebar_class').html();
if (has_sidebar.length > 1)
{
  $('div.sidebar_class').addClass('some_class');
  $('div.right_content_of_sidebar').addClass('some_other_class');
}

but there are a thousand solutions! even with ci.

the js maybe wrong, i don't check nothing