javascript - How to group and apply class for specific within based on li:child?

Question

Please find my ul li here, This li is working for horizontal tab using a bootstrap tab. I'm trying to apply a class; when the 2nd and 3rd li have the class active, I want to apply a style class on the 1st li. simlarly for next 3 li and rest also. I've tried with jquery but didn't succeed.

<ul id="myTab" class="nav-tabs">
  <li class="side-menu-grp"><a href="#">Group One</a></li>
  <li><a href="#" data-toggle="tab">List One</a></li>
  <li><a href="#" data-toggle="tab">List Two</a></li>

  <li class="side-menu-grp"><a href="#">Group Two</a></li>
  <li><a href="#" data-toggle="tab">List One</a></li>
  <li><a href="#" data-toggle="tab">List Two</a></li>

  <li class="side-menu-grp"><a href="#">Group Three</a></li>
  <li><a href="#" data-toggle="tab">List One</a></li>
  <li><a href="#" data-toggle="tab">List Two</a></li>
</ul>

Answer 1

我认为这就是你想要的：

$('.active').prev('.side-menu-grp').addClass('class');

它选择带有 class 的元素active（li如果您不重用该类，则为 s）并找到带有 class 的第一个先前的兄弟元素side-menu-grp并将您想要的类添加到它。