LinkedListMethods.js

class Node {
  constructor(value) {
    this.value = value;
    this.next = null;
  }
}

class LinkedList {
  constructor() {
    this.head = null;
  }
};


/**
 * Given a LinkedList and a value, return true if the value exists in the list, if not return false
 */
const doesValueExist = (list, value) => {
  // grab head as variable
  let node = list.head;
  // as long as a node exists, traverse the list
  while (node) {
    // if we found the value, return true!
    if (node.value === value) {
      return true;
      // else redefine node as the node.next and continue traversing
    } else {
      node = node.next;
    }
  }
  // if we got here, we're at the end of the list and have not found our value, return false;
  return false;
}

/**
 * Given a LinkedList and a value, add the value (as a new node) on the list as the head
 */
const addToHead = (list, value) => {
  // create new node to insert
  const newHead = new Node(value)
  // grab old head as a variable
  let oldHead = list.head;
  // redefine new head
  list.head = newHead;
  newHead.next = oldHead;
}

/**
 * Given a LinkedList and a value, add the value (as a new node) on the list as the tail
 */
const addToTail = (list, value) => {
  // create new node to insert
  const newTail = new Node(value)
  // grab head as variable
  let node = list.head;
  // if there is no head, set new node as head and return
  if (!node) {
    return list.head = newTail;
  }
  // as long as there is a node.next keep traversing. if there is NO node.next, we are at the tail.
  while (node.next) {
    node = node.next;
  }
  // set the tai's next as the new tail
  node.next = newTail;
};

/**
 * Given a LinkedList, a value, and an index, insert the value (as a new node) in the list at the given index
 */
const insertAtIndex = (list, value, index) => {
  // create new node to insert
  const newNode = new Node(value);
  // start counter to keep track of current index
  let counter = 0;
  // grab head as variable
  let node = list.head;
  // traverse until we are at the node BEFORE the index we want to insert
  while (counter < index) {
    counter++;
    if (!node.next) {
      // handle edge case of index is greater than available nodes
      throw new Error('No node at the given index');
    }
    node = node.next;
  }
  // when we are at index BEFORE the index we want to insert, assign new node's next as the node.next's node
  newNode.next = node.next;
  // reassign node.next as the new node
  node.next = newNode;
};