Method append

chapter03/util/LinkedList.js:16–27

(value)

  }

  append(value) {
      let node = new Node(value);
      // if list is empty
      if (!this.head) {
          this.head = node;
          this.tail = node;
      }
      else {
          this.tail.next = node;
          this.tail = node;
      }
  }

  prepend(value) {
      let node = new Node(value);