Usage of the ternary "?:" operator with functions listening to click events
Let's do some fixing. First, this is how you pass optional (non-boolean) parameters in JS (the Good Waytm):

addFooListeners = function (panelType, handlers) {
    handlers        = handlers        || {};
    handlers.show   = handlers.show   || showFoo;
    handlers.hide   = handlers.hide   || hideFoo;
    handlers.commit = handlers.commit || commitFoo;


The above can be rewritten in a neater way using jQuery (not sure what the name of YUI equivalent to extend is):

handlers = $.extend({
    show  : showFoo, 
    hide  : hideFoo, 
    commit: commitFoo
}, handlers || {})


Now, using eval for this code is criminal. Say the object ns refers to is module, then you can do this instead of eval:

YAHOO.util.Event.addListener("show" + panelType, "click", handlers.show, module["panel_" + panelType], true);
YAHOO.util.Event.addListener("hide" + panelType, "click", handlers.hide, module["panel_" + panelType], true);
YAHOO.util.Event.addListener("commit" + panelType, "click", handlers.commit, module["panel_" + panelType], true);


Now, as you can see, you are assigning a lot of events in a similar fashion. Did you think of defining an addPanelListener function within your function?

function addPanelListener (event, panelType, handler) {
    YAHOO.util.Event.addListener(event + panelType, "click", handler, module["panel_" + panelType], true);
} 

addPanelListener("show"  , panelType, handlers.show);
addPanelListener("hide"  , panelType, handlers.hide);
addPanelListener("commit", panelType, handlers.commit):


Hope it helps.