add class via jquery but only when not exists

Question

I would like to add a class (class=\"bbox\") to a ul-list but only if no class exists. This is what i have so far. How do I check with jquery if a class exists in the ul-tag

Answer 1

Concisely:

// fine, because nothing happens if 
// there are no matching elements
$("ul[class='']").addClass("bbox");