text: // SOURCE: http://blog.benoitvallon.com/data-structures-in-javascript/data-structures-in-javascript-all-the-code/
  
  function Node(data) {
    this.data = data;
    this.next = null;
  }
  
  function SinglyLinkedList() {
    this.head = null;
    this.tail = null;
    this.numberOfValues = 0;
  }
  
  SinglyLinkedList.prototype.add = function(data) {
    var node = new Node(data);
    if(!this.head) {
      this.head = node;
      this.tail = node;
    } else {
      this.tail.next = node;
      this.tail = node;
    }
    this.numberOfValues++;
  };
  SinglyLinkedList.prototype.remove = function(data) {
    var previous = this.head;
    var current = this.head;
    while(current) {
      if(current.data === data) {
        if(current === this.head) {
          this.head = this.head.next;
        }
        if(current === this.tail) {
          this.tail = previous;
        }
        previous.next = current.next;
        this.numberOfValues--;
      } else {
        previous = current;
      }
      current = current.next;
    }
  };
  SinglyLinkedList.prototype.insertAfter = function(data, toNodeData) {
    var current = this.head;
    while(current) {
      if(current.data === toNodeData) {
        var node = new Node(data);
        if(current === this.tail) {
          this.tail.next = node;
          this.tail = node;
        } else {
          node.next = current.next;
          current.next = node;
        }
        this.numberOfValues++;
      }
      current = current.next;
    }
  };
  SinglyLinkedList.prototype.traverse = function(fn) {
    var current = this.head;
    while(current) {
      if(fn) {
        fn(current);
      }
      current = current.next;
    }
  };
  SinglyLinkedList.prototype.length = function() {
    return this.numberOfValues;
  };
  SinglyLinkedList.prototype.print = function() {
    var string = '';
    var current = this.head;
    while(current) {
      string += current.data + ' ';
      current = current.next;
    }
    console.log(string.trim());
  };
  
  var singlyLinkedList = new SinglyLinkedList();
  singlyLinkedList.print(); // => ''
  singlyLinkedList.add(1);
  singlyLinkedList.add(2);
  singlyLinkedList.add(3);
  singlyLinkedList.add(4);
  singlyLinkedList.print(); // => 1 2 3 4
  console.log('length is 4:', singlyLinkedList.length()); // => 4
  singlyLinkedList.remove(3); // remove value
  singlyLinkedList.print(); // => 1 2 4
  singlyLinkedList.remove(9); // remove non existing value
  singlyLinkedList.print(); // => 1 2 4
  singlyLinkedList.remove(1); // remove head
  singlyLinkedList.print(); // => 2 4
  singlyLinkedList.remove(4); // remove tail
  singlyLinkedList.print(); // => 2
  console.log('length is 1:', singlyLinkedList.length()); // => 1
  singlyLinkedList.add(6);
  singlyLinkedList.print(); // => 2 6
  singlyLinkedList.insertAfter(3, 2);
  singlyLinkedList.print(); // => 2 3 6
  singlyLinkedList.insertAfter(4, 3);
  singlyLinkedList.print(); // => 2 3 4 6
  singlyLinkedList.insertAfter(5, 9); // insertAfter a non existing node
  singlyLinkedList.print(); // => 2 3 4 6
  singlyLinkedList.insertAfter(5, 4);
  singlyLinkedList.insertAfter(7, 6); // insertAfter the tail
  singlyLinkedList.print(); // => 2 3 4 5 6 7
  singlyLinkedList.add(8); // add node with normal method
  singlyLinkedList.print(); // => 2 3 4 5 6 7 8
  console.log('length is 7:', singlyLinkedList.length()); // => 7
  singlyLinkedList.traverse(function(node) { node.data = node.data + 10; });
  singlyLinkedList.print(); // => 12 13 14 15 16 17 18
  singlyLinkedList.traverse(function(node) { console.log(node.data); }); // => 12 13 14 15 16 17 18
  console.log('length is 7:', singlyLinkedList.length()); // => 7
  