SOURCE

function Node(item) {
  this.item = item;
  this.next = null;
}

function LinkedList() {
  this.length = 0;
  this.head = null;
}

// 添加元素到链表尾部
LinkedList.prototype.append = function(item) {
  if (this.length === 0) {
    this.head = item;
  } else {
  	var current = this.head;
    while(current.next) {
      current = current.next;
    }
    current.next = item;
  }
  this.length++;
}
// 向单向链表中某个位置插入元素
LinkedList.prototype.insert = function(position, item) {
  if (position === 0) {
    var current = this.head;
    this.head = item;
    this.head.next = current;
  } else {
    var current = this.head;
    var prevent = current;
    var index = 0;
    while(position > index) {
      prevent = current;
      current = current.next;
      index++;
    }
    item.next = current;
    prevent.next = item;
  }
  this.length++;
}
// 寻找某个元素在单向链表中的位置
LinkedList.prototype.indexOf = function(item) {
  var current = this.head;
  var index = 0;
  while(current.next) {
    if (current.item === item) {
      return index;
    }
    current = current.next;
    index++;
  }
  return -1;
}
// 移除给定的元素
LinkedList.prototype.remove = function(item) {
  var current = this.head;
  var prevent = current;
  var index = 0;
  while(current.next) {
    if (current.item === item) {
      if (index === 0) {
        this.head = current.next;
      } else {
        prevent.next = current.next;
      }
      this.length --;
      return;
    }
    prevent = current;
    current = current.next;
    index ++;
  }
  if (current.item === item) {
    prevent.next = null;
    this.length--;
  }
} 
// 移除单向链表中某个位置的元素
LinkedList.prototype.removeAt = function(position) {
  var current = this.head;
  var prevent = current;
  var index = 0;

  while(current.next) {
    if (position === index) {
      if (index === 0) {
        this.head = current.next;
      } else {
        prevent.next = current.next;
      }
      this.length --;
      return;
    }
    prevent = current;
    current = current.next;
    index ++;
  }
  if (position === index) {
    prevent.next = null;
    this.length --;
  }
}
// 获取单向链表的头部
LinkedList.prototype.getHead = function() {
  return this.head;
}
// 检查单向链表是否为空，为空则返回true
LinkedList.prototype.isEmpty = function() {
  return this.length === 0;
}
// 将链表所有内容以字符串输出
LinkedList.prototype.toString = function() {
  var current = this.head;
  var content = current.item.toString();
  while(current.next) {
    current = current.next;
    content += current.item.toString();
  }
  return content;
}
// 返回单向链表长度
LinkedList.prototype.size = function() {
  return this.length;
}

var n1 = new Node(9);
var n2 = new Node(8);
var n3 = new Node(6);
var l = new LinkedList();
l.append(n1);
l.append(n2);
l.insert(1, n3);
console.log(l.toString());
console.log(l.indexOf(6));
l.remove(8);
console.log(l.toString());
// l.insert(0, n1);
// console.log(l.toString());
// l.removeAt(2);
// console.log(l.toString());
// console.log(l.getHead());
// console.log(l.isEmpty());
// console.log(l.size());