window.onload方法被覆盖了，把两块代码放一块，或者用addEventListener

GlobalEventHandlers.onload

貌似window.onload在同一个html引入的js文件里只能写一次。

你这样写试试：（我只是简略的写了代码，没测试，自己测测改改吧）

            window.onload = function(){
                //父选项卡控制
                tab("tab_t","li","tab_c","a_b","act","p","onclick");
                //子选项卡控制
                tab("bab_t","li","bab_c","b_b","bct","p","onclick");
            };
        
             function tab(tab_t,tab_t_tag,tab_c,tab_c_li,tab_t_li,tag_c_tag,evt){
                var tab_t = document.getElementById(tab_t);
                var tab_t_li = tab_t.getElementsByTagName(tab_t_tag);
                var tab_c = document.getElementById(tab_c);
                var tab_c_li = document.getElementsByClassName(tab_c_li);
                var len = tab_t_li.length;
                var i=0;
                for(i=0; i<len; i++){
                    tab_t_li[i].index = i;
                    tab_t_li[i][evt] = function(){
                        for(i=0; i<len; i++){
                            tab_t_li[i].className = '';
                            tab_c_li[i].className = 'hide '+tab_c_li+'';
                        }
                        tab_t_li[this.index].className = ''+tab_t_li+'';
                        tab_c_li[this.index].className = ''+tab_c_li+'';
                    }
                }
            }