js将数组根据条件分组

//将数组根据条件分组
function getTreeDateByParam(list, param, fun){
    var data = {};
    if(list && list.length > 0){
        for(var i = 0; i < list.length; i++){
            if(param){
                var res = list[i][param]
            }else if(fun){
                var res = fun(list[i]);
            }
            if(data[res]){
                data[res].push(list[i]);
            }else{
                data[res] = [list[i]];
            }
        }
    }
    return data;
}

var map = getTreeDateByParam(vacc,'vaccCode');

vacc[0]的vaccCode有值，另外两个是未定义的