understandable singly linked list in javascript

linked-list.js

// list node constructor
function ListNode(val) {
  this.next = null;
  this.value = val;
}


const MyLinkedList = function () {
  this.head = null; // the head of the linked lsit
  this.size = 0;    // use the size to have addtional useful validation
};

MyLinkedList.prototype.get = function (index) {
  
  if (this.head == null || index >= this.size) return -1;

  let cur = this.head;

  while (index > 0) {
    cur = cur.next;
    index--;
  }

  return cur.value;
};


MyLinkedList.prototype.addAtHead = function (val) {
  // init the list node
  const newNode = new ListNode(val);
    
  if (this.head == null) {
    this.head = newNode;
  } else {
    newNode.next = this.head;
    this.head = newNode;
  }
  this.size++;
};


MyLinkedList.prototype.addAtTail = function (val) {
  const newNode = new ListNode(val);
    
  if (this.head == null) this.head = newNode;
  
  else {
    let cur = this.head;
    while (cur.next) cur = cur.next;
    cur.next = newNode;
  }
  this.size++;
};


MyLinkedList.prototype.addAtIndex = function (index, val) {
  if (index < 0 || index > this.size) return;

    
  const newNode = new ListNode(val);

    
  if (index == 0 && this.head == null) {

      this.head = newNode;
  } else if (index == 0) {
      newNode.next = this.head;
      this.head = newNode;
  } else {
    let cur = this.head;
    while (index > 1) {
      cur = cur.next;
      index--;
    }

    if (cur.next) {
      newNode.next = cur.next;
    }

    cur.next = newNode;
  }
  this.size++;
};


// delete at index
MyLinkedList.prototype.deleteAtIndex = function (index) {
  
  // do some checks (valid enterd index, valid enterd index with the size, if there any elements) 
  if (index < 0 || index >= this.size || this.head == null) {
    return;
  } 
  
  
  else if (index == 0) {
    this.head = this.head.next;
  } 
    
  else {
    // point to the head of the linked list
    let cur = this.head;
    
    // traversal the linked list until we find the the node is before the current index
    while (index > 1) {
      cur = cur.next;
      index--;
    }
    
    // delete the current index
    cur.next = cur.next.next;
  }
    
  // decrease the size
  this.size--;
};

good