bootstrap和JS实现下拉菜单

// bootstrap下拉菜单
<div class="btn-group">
  <button id="button_text" type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
    Action <span class="caret"></span>
  </button>
  <ul class="dropdown-menu">
    <li><a href="#" class="a-1">Action</a></li>
    <li><a href="#" class="a-1">Another action</a></li>
    <li><a href="#" class="a-1">Something else here</a></li>
    <li role="separator" class="divider"></li>
    <li><a href="#" class="a-1">Separated link</a></li>
  </ul>
</div>

// 点击拉下框选项，替换展示内容
$(".a-1").click(function () {
    var val = $(this).html();
    $("#button_text").text(val)
})