bxslider无法正常工作

Question

我正在玩bxslider，有时它可以正常工作，其他情况则不然。我认为它与javascript错误有关，它说：TypeError: Has no method goToNextSlider();我不是jQuery的专家......

var slider = $('.bxslider').bxSlider({
    controls: false,
    pager: false
  });

  $('#pronext').click(function(){
    slider.goToNextSlide();
    return false;
  });

  $('#proprev').click(function(){
    slider.goToPrevSlide();
    return false;
  });

HTML

    <div class='row'>
      <div class='large-1 columns'>
        <a href='' id='proprev'><img alt="Prev" class="testimonials__navigation__arrow" src="/assets/prev.png" /></a>
      </div>
      <div class='large-10 columns'>
        <ul class='bxslider'>
          <li>1</li>
          <li>2</li>
        </ul>
      </div>
      <div class='large-1 columns'>
        <a href='' id='pronext'><img alt="Next" class="testimonials__navigation__arrow" src="/assets/next.png" /></a>
      </div>
    </div>

提前致谢.. 启