LinkedList.js

/** Linked List */

function LinkedList() {
  let length = 0;
  let head = null;

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

  this.size = function () {
    return length;
  }

  this.head = function() {
    return head;
  }

  this.add = function(element) {
    let node = new Node(element);
    if (head === null) {
      head = node;
    } else {
      let currentNode = head;

      while(currentNode.next) {
        currentNode = currentNode.next;
      }

      currentNode.next = node;
    }
    length ++;
  }// End add

  this.remove = function(element) {
    let currentNode = head;
    let previousNode;

    if (currentNode.element === element) {
      head = currentNode.next;
    } else {
      while(currentNode.element !== element) {
        previousNode = currentNode;
        currentNode = currentNode.next;
      }
      previousNode.next = currentNode.next;
    }
    length --;
  }// End remove

  this.isEmpty = function() {
    return length === 0;
  }// End isEmpty

  this.indexOf = function(element) {
    let currentNode = head;
    let index = -1;

    while(currentNode) {
      index++;
      if (currentNode.element === element) {
        return index;
      }
      currentNode = currentNode.next;
    }
    return -1;
  }// End indexOf

  this.elementAt = function(index) {
    let currentNode = head;
    let count = 0;
    while(count < index) {
      count++;
      currentNode = currentNode.next;
    }
    return currentNode.element;
  }//End elementAt

  this.addAt = function(index, element) {
    let node = new Node(element);
    let currentNode = head;
    let previousNode;
    let currentIndex = 0;
    if (index > length) {
      return false;
    }
    if (index === 0) {
      node.next = currentNode;
      head = node;
    } else {
      while(currentIndex < index) {
        currentIndex++;
        previousNode = currentNode;
        currentNode = currentNode.next;
      }
      node.next = currentNode;
      previousNode.next = node;
    }
    length++;
  }// End addAt

  this.removeAt = function(index) {
    let currentNode = head;
    let previousNode;
    let currentIndex = 0;
    if (index < 0 || index >= length) {
      return null;
    }
    if (index === 0) {
      head = currentNode.next;
    } else {
      while(currentIndex < index) {
        currentIndex++;
        previousNode = currentNode;
        currentNode = currentNode.next;
      }
      previousNode.next = currentNode.next;
    }
    length--;
    return currentNode.element;
  }// End removeAt
}// End LinkedList

const conga = new LinkedList();
conga.add('kiten');
conga.add('Puppy');
conga.add('Dog');
conga.add('Cat');
conga.add('Fish');
console.log(conga.size());
console.log(conga.removeAt(3));
console.log(conga.elementAt(3));
console.log(conga.indexOf('Puppy'));
console.log(conga.size());