这个方法摘自《javascript设计模式》，因为作者对YUI非常熟悉，所以方法的的思路和YUI一样。方法如下：

function extend(subClass,superClass){

    var F = function(){};

     F.prototype = superClass.prototype;

     subClass.prototype = new F();

     subClass.prototype.constructor = subClass;

      subClass.superclass = superClass.prototype;

      if(superClass.prototype.constructor == Object.prototype.constructor){

         superClass.prototype.constructor = superClass;

      }

}