Suggested solution for Data Structures: Add Elements at a Specific Index in a Linked List

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Solution 
function LinkedList() {
  var length = 0;
  var head = null;

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

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

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

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

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

      currentNode.next = node;
    }
    length++;
  };

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

Challenge: Add Elements at a Specific Index in a Linked List

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