I'm using this bit of jQ to add a class to two different elements based on the class of another (parent/grandparent, etc) element:

$(document).ready(function(){
    var containerClass = $('#main-content').attr('class');
    $('#nav-primary li#'+containerClass).addClass('active');
    $('#aux-left div[id$='+containerClass+']').addClass('active');
});

Brilliant, but I have two problems with it:

First, when there's no class at all in <div id="main-content">, the 'active' class is added to all the #nav-primary LIs, and also to all the #aux-left DIVs; how can I modify this so that in the absence of any class on #main-content, do nothing?

Second, how can I target only the first or second of multiple classes to store in the 'containerClass' variable, e.g., <div id="main-content" class="apples bananas">?

Very much appreciated! svs