A simple jQuery plugin that selects all options on a <select multiple>

jquery.selectall.js

(function ($){
    $.fn.selectAll = function (selector) {
        var sel = selector || 'option';

        $(sel, this).each(function () {
            if (this.disabled) {
                this.selected = false;
            } else {
                this.selected = true;
            }
        });
    }
}(jQuery));