Method shift

lib/Deque.js:18–27

* removes and returns the first element from the queue * @return {any} [description]

()

   * @return {any} [description]
   */
  shift() {
    if (this.length === 0) {
      return undefined;
    }

    const node = this._list.head;
    this._list.remove(node);

    return node.data;
  }

  /**
   * adds one elemts to the beginning of the queue