A simple LinkedList implementation using JavaScript

linkedlist.js

LinkedListItem.prototype = {
  getId:      function()        { return this.id; },
  getNext:    function()        { return (this.next !== undefined || null) ? this.next : null; },
  setNext:    function(next)    { this.next = next; },
  unsetNext:  function()        { delete this.next; },
  getPrev:    function()        { return this.prev; },
  isLast:     function()        { return (this.next === undefined || this.next === null) ? true : false; },
  isFirst:    function()        { return this.isInitial; },
  getContent: function()        { return this.content; },
  setContent: function(content) { this.content = content; }
}


LinkedList.prototype = {
  getFirst:   function() { return this.initialNode; },
  getLast:    function() {
    var node = this.getFirst();
    if (node.getNext() === null) return node;
    while (node.getNext() !== null) node = node.getNext();
    return node;
  },

  addItem:    function(content) {
    if (this.getFirst() === null) {
      this.initialNode = new LinkedListItem(content, true, this.length, undefined);
      return;
    }
    var node = this.getLast();
    node.setNext(new LinkedListItem(content, false, this.length, node));
    this.length++;
  },

  findItem:   function(id) {
    var node = this.getFirst();
    if (node.id === id) return node;
    while (node.getNext() !== null) {
      node = node.getNext();
      if (node.id === id) return node;
    }
    return undefined;
  }
}


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

function LinkedListItem(content, isInitial, id, previous) {
  this.content = content;
  this.isInitial = isInitial;
  this.id = id;
  this.prev = previous;
}