刚接触js， extjs 中extend的代码如下, 其中这段相当困惑，请老大们指点下

                if(typeof sp == 'object'){
                    overrides = sp;
                    sp = sb;
                    sb = function(){sp.apply(this, arguments);};
                }

当sp为ojbect时，sp 指向 sb,
sb = function(){sp.apply(this, arguments);};
其中的this应该指向sp吧，而sp已经指向sb，这样出来，到底有什么用意？
其中的arguments也不是特别明白，先谢过



附：extend代码：
=======================================================
       extend : function(){
            // inline overrides
            var io = function(o){
                for(var m in o){
                    this[m] = o[m];
                }
            };
            return function(sb, sp, overrides){
                if(typeof sp == 'object'){
                    overrides = sp;
                    sp = sb;
                    sb = function(){sp.apply(this, arguments);};
                }
                var F = function(){}, sbp, spp = sp.prototype;
                F.prototype = spp;
                sbp = sb.prototype = new F();
                sbp.constructor=sb;
                sb.superclass=spp;
                if(spp.constructor == Object.prototype.constructor){
                    spp.constructor=sp;
                }
                sb.override = function(o){
                    Ext.override(sb, o);
                };
                sbp.override = io;
                Ext.override(sb, overrides);
                return sb;
            };
        }()
--
修改:oicsunnyrain FROM 211.140.10.*
FROM 211.140.10.*