Наследование в javascript

var BaseModalMethods = {
    init : function ()
    {
        console.log('BaseModalMethods.init');
    },
    modal : function ()
    {
        this.beforeShow();
        console.log('BaseModalMethods.modal');
    }
};

function SimpleModalPlugin() {
    this.beforeShow = function() {
        console.log('SimpleModalPlugin.beforeShow');
    }
}

SimpleModalPlugin.prototype = BaseModalMethods;

var a = new SimpleModalPlugin();
a.modal();

Вывод:

SimpleModalPlugin.beforeShow
BaseModalMethods.modal