js原型鏈函數(shù)覆蓋問題

同一個原型鏈函數(shù)，傳入不同參數(shù)，得出不同的結(jié)果，但后一個函數(shù)覆蓋了前一個函數(shù)，兩個函數(shù)輸出相同的結(jié)果，此為排序的示例，排序優(yōu)先級為age->sex->id
var arr = [

        {"name":"aa","id":1000,"sex":0,"age":28},
        {"name":"bb","id":1001,"sex":1,"age":18},
        {"name":"cc","id":1002,"sex":0,"age":18},
        {"name":"cc","id":1003,"sex":1,"age":18}
        
      ];
      
      //1.升序

function upsort(first,second,third){

return function(a,b){
    var v1 = a[first];
    var v2 = b[first];
    var res = v1 - v2;
    if(res == 0){
        upsort(first,second,third);
        var v3 = a[second];
        var v4 = b[second];
        var res2 = v3 - v4;
        return res2;
        if(res2 == 0){
            upsort(first,second,third);
            var v5 = a[third];
            var v6 = b[third];
            var res3 = v5 - v6;
            return res3;
        }
    }
    return res;
}

}

    //2.降序

function downsort(first,second,third){

return function(a,b){
    var v1 = a[first];
    var v2 = b[first];
    var res = v2 - v1;
    if(res == 0){
        downsort(first,second,third);
        var v3 = a[second];
        var v4 = b[second];
        var res2 = v4 - v3;
        return res2;
        if(res2 == 0){
            downsort(first,second,third);
            var v5 = a[third];
            var v6 = b[third];
            var res3 = v6 - v5;
            return res3;
        }
    }
    return res;
}

}

function sortPlugin(){}
sortPlugin.prototype.str = 1; //1為升序，2為降序，默認為升序
sortPlugin.prototype.sortWay = function(str = this.str){

if(str == 1){
    console.log(arr.sort(upsort("age","sex","id")));
}else if(str == 2){
    console.log(arr.sort(downsort("age","sex","id")));
}

}

var sp = new sortPlugin();
sp.sortWay();

sp2.sortWay(2);

單獨運行兩個函數(shù)是沒問題的，不知道哪里出了問題，原型鏈還沒有吃透