[原创]一个js函数重载功能

var _ = {
    type2string:{},
    type:function(s){
        return s == null ? 'empty' : (_.type2string[Array.prototype.toString.call(s)] || 'object');
    },
    defined:function(type,f){
        var fn = function(){
            var args = Array.prototype.slice.call(arguments);
            var i = 0, p , ff = fn['_'];
            while(p = args[i++]){ ff = ff[_.type(p)]; }
            if(!ff || !ff.fn){ 
                ff = fn['_'];
                if(ff && ff.fn){
                    return ff.fn.apply(fn,args);
                }
                throw new Error('function undefined!') 
            }
            return ff.fn.apply(fn,args);
        };
        _._defined(type,fn,f);
        fn['defined'] = function(type,f1){ return _._defined(type,fn,f1); };
        return fn;
    },
    _defined:function(type,fn,source){
        var types = fn['_'];
        if(!types){ types = fn['_'] = {} }
        if(_.type(type)=='function'){
            types['fn'] = type;
            return fn;
        }
        type.replace(/[^,]+/g,function(t){
            types[t] = types[t] || {};
            types = types[t];
        });
        types['fn'] = source;
        return fn;
    }
};
('Object,Function,String,Number,Boolean,Date,RegExp').replace(/[^,]+/g,function(a){
    _.type2string['[object ' + a + ']'] = a.toLowerCase();
});
var a = _.defined(function(a,b){
    //alert(['string|number']);
    alert([a,b])
}).defined('string,string',function(s1,s2){
    alert(['string|string',s1,s2]);
}).defined('string,object',function(s,o){
    alert(['string|object',s,o])
});
a('1');
a('1','2');
a('1',{});
a('1',true);