javascript中在鏈表中向前（向后）移動n個節(jié)點

/**
 * 實現(xiàn)在鏈表中向前移動n個節(jié)點和向后移動n個節(jié)點
 * 
 * */

//鏈表節(jié)點
function Node(element){
    this.element = element;
    this.next = null;
    this.previous = null;
}

//鏈表
function LList(){
    this.head = new Node('head');
    this.find = find;
    this.insert = insert;
    this.display = display;
    this.remove = remove;
    this.findLast = findLast;
    this.dispReverse = dispReverse;
    //當(dāng)前節(jié)點就是頭節(jié)點
    this.currentNode = this.head;
    //從鏈表開頭向前移動n個節(jié)點
    this.advance = advance;
    //從鏈表某個節(jié)點向后回退n個節(jié)點
    this.back = back;
    //顯示當(dāng)前節(jié)點
    this.show = show;
}

//倒序輸出鏈表中的所有節(jié)點
function dispReverse(){
    var currNode = this.head;
    currNode = this.findLast();
    while (!(currNode.previous == null)){
        document.write(currNode.element + ' ');
        currNode = currNode.previous;
    }
}

//找到最后一個節(jié)點
function findLast(){
    var currNode = this.head;
    while (!(currNode.next == null)){
        currNode = currNode.next;
    }
    return currNode;
}

//刪除某一個節(jié)點
function remove(item){
    var currNode = this.find(item);
    if(!(currNode.next == null)){
        currNode.previous.next = currNode.next;
        currNode.next.previous = currNode.previous;
        currNode.next = null;
        currNode.previous = null;
    }
}

//打印所有鏈表節(jié)點
function display(){
    var currNode = this.head;
    while (!(currNode.next == null)){
        document.write(currNode.next.element + ' ');
        currNode = currNode.next;
    }
}

//找到某一個節(jié)點
function find(item){
    var currNode = this.head;
    while (currNode.element != item){
        currNode = currNode.next;
    }
    return currNode;
}

//插入某一個節(jié)點
function insert(newElement , item){
    var newNode = new Node(newElement);
    var current = this.find(item);
    newNode.next = current.next;
    newNode.previous = current;
    current.next = newNode;
}

//在鏈表中向前移動n個節(jié)點
function advance(n){
    while ((n>0) && !(this.currentNode.next==null)){
        this.currentNode = this.currentNode.next; 
        n--
    }
}

//在鏈表中向后移動n個節(jié)點
function back(n){
    while (n>0 && !(this.currentNode.element=='head')){
        this.currentNode = this.currentNode.previous;
        n--;
    }
}

//顯示當(dāng)前節(jié)點
function show(){
    document.write(this.currentNode.element);
}

var cities = new LList();
cities.insert('Conway','head');
cities.insert('Russellville', 'Conway');
cities.insert('Carlisle', 'Russellville');
cities.insert('Alma' , 'Carlisle');
cities.insert('dezhou' , 'Alma');
cities.insert('alasijia' , 'dezhou');
cities.display();
document.write('<br>');

cities.show();
cities.advance(4);
document.write('<br>');
cities.show();
cities.back(2);
document.write('<br>');
cities.show();