How to package up functionality in Javascript?

there's absolutely no reason why your Widget's can not be build from Component's.

Now I don't know what framework you have in place so lets go with something generic.

function HideableComponent(el) {
    this.show = function() {
         $(el).show();
    }

    this.hide = function() {
        $(el).hide();
    }
}

function LoadableComponent(el) {
    this.load = function(url) {
        $(el).load(url);
    }
}

var Components = {
    "Loadable": LoadableComponent,
    "Hideable": HideableComponent
}

function SomeUIWidget(el) {
    var hide = new Component.Hideable(el),
        load = new Component.Loadable(el);

    $.extend(true, this, hide, load);

    ...
}

Now the examples are trivial. presumably the components would be more then very thin wrappers around jQuery functions and have inbuild configs, customability, automation and validation.

The point is there is no reason why you can't have your widgets draw upon components no matter how trivial they are.

As long as the components make your code more DRY and more readable / maintainable then you can make them as small and trivial as you want.

One reason you may even want to do this is to abstract away the use of jQuery as your DOM manipulation library and allow a generic set of Components that can be loaded as jQueryComponents, MooToolsComponents etc whilst keeping a common API.

Now this may start to border on over-engineering. You need to find a good balance for your own project.

As for a rotator meta class maybe something like this

function RotatorComponent(container) {
    var children = $(container).children(),
        curr = children.first();

    this.rotate = function(draw) {
         curr = curr.next();
         draw(curr);
    }
}