请问为什么console.log(listToArray(arrayToList([1,2,3])));运行结果是[1]而不是[1,2,3]呢，第二个函数问题出在哪里

function arrayToList(arr){
    var list = {};
    list['value'] = arr[0];
    if (arr.length > 1) {
        list['rest'] = arrayToList(arr.slice(1))
    }else{
        list['rest'] = null;
    }
    return list;
}

function listToArray(list){
    var arr = [];
    for(var key in list){
        if (key =='value') {
            console.log(1)
            arr.push(list[key]);
        }else if (key == 'rest' && list.rest != null) {
            console.log(2);
            arr.concat(listToArray(list.rest));
        }
    }
                console.log(arr);
    return arr;
}