JSFiddle - React, Tailwind, and code Playground

HTML

<b>ресультат hasClass: </b><span id="res"></span>



<div class="wapper_important_news clearfix">

  <div class="i_n_static fs36 regular">ВАЖНО!</div>

  <div data-rel="n" class="i_n_block clearfix">

    <div class="left">
      <div class="i_n_date fs13 light">DATE</div>
    </div>

    <div class="right">
      <div class="table-cell">

        <a href="#href" class="underline">
          <div class="i_n_title fs16 bold">TEXT_HREF</div>
        </a>
        <div class="i_n_desc fs16 light">TEXT</div>

      </div>
    </div>

  </div>
  <div class="i-n-control">
    <div class="left"></div>
    <div class="right"></div>
  </div>
</div>

JavaScript

var a = $(".i_n_block:visible");
$(".wapper_important_news").height(a.next().find(".right").height());
$("#res").text(a.next().hasClass('i_n_block'))