js多态

function addMethod(object,name,fn){
    var old=object[name];
    object[name]=function(){
         if(fn.length==arguments.length)
            return fn.apply(this,arguments);
         else if(typeof old=='function')
            return old.apply(this,arguments);
    };
}            

使用：
var gc={};
addMethod(gc,'whatever',function(){})
addMethod(gc,'whatever',function(a){})
addMethod(gc,'whatever',function(a,b){})

//只与参数个数有关