Bootsrap 3下拉子菜单链接在移动视图中不起作用

<div class="dropdown">
  <button class="btn btn-default dropdown-toggle" type="button" id="dropdownMenu" data-toggle="dropdown" aria-haspopup="true" aria-expanded="true">
    Dropdown
    <span class="caret"></span>
  </button>
  <ul class="dropdown-menu" aria-labelledby="dropdownMenu">
    <li><a href="#">Link 1</a></li>
    <li><a href="#">Link 2</a></li>
    <li><a href="#">Link 3</a></li>
  </ul>
</div>

$(document).ready(function(){
  if($(window).width() < 768){
    $('#dropdownMenu').click(function(){
      $(this).next('.dropdown-menu').slideToggle();
    });
  }
});