custom-select.js

// plugin example
(function($){
    // custom select class
    function CustomSelect(item, options) {
        this.options = $.extend({
            foo: 'bar'
        }, options);
        this.item = $(item);
        this.init();
    }
    CustomSelect.prototype = {
        init: function() {
            this.item.css({opacity:0.5});
        },
        resetOpacity: function() {
            this.setOpacity('');
        },
        setOpacity: function(opacity) {
            this.item.css({opacity:opacity});
        }
    }

    // jQuery plugin interface
    $.fn.customSelect = function(opt) {
        var args = Array.prototype.slice.call(arguments, 1);
        return this.each(function() {
            var item = $(this), instance = item.data('CustomSelect');
            if(!instance) {
                // create plugin instance if not created
                item.data('CustomSelect', new CustomSelect(this, opt));
            } else {
                // otherwise check arguments for method call
                if(typeof opt === 'string') {
                    instance[opt].apply(instance, args);
                }
            }
        });
    }

}(jQuery));

// plugin testing
$('select').customSelect();