In Prototype JS you get given an element, but in jQuery you get given a list of elements, which makes things confusing when selecting a class of elements in Prototype JS or jQuery

jQuery, Oh so simple.

    $("p").click(function () { 
      $(this).something(); 
    });

Prototype JS...

$$("a.treeItem").each(function(n) {
    Event.observe(n, "click", function() { 
   	    n.something(); 
    });
});