JSFiddle - React, Tailwind, and code Playground

HTML

<select id="WorkflowLevel" class="form-control" name="show_text_area" onchange="WorkflowLevel(this)">
    <option value="0">Select</option>
    <option value="1">1</option>
    <option value="2">2</option>
    <option value="3">3</option>
</select>

<div id="OneLevel" class="Level">1</div>
<div id="TwoLevel"  class="Level">2</div>
<div id="ThreeLevel"  class="Level">3</div>

JavaScript

$(".Level").hide();

function WorkflowLevel(obj) {
  var selectBox = obj;
  var selected = selectBox.options[selectBox.selectedIndex].value;

  $(".Level").hide();

  switch (selected) {
    case '0':
      $(".Level").hide();
      break;
    case '1':
      $(".Level").hide();
      $("#OneLevel").show();
      break;
    case '2':
      $(".Level").hide();
      $("#TwoLevel").show();
      break;
    case '3':
      $(".Level").hide();
      $("#ThreeLevel").show();
      break;
  }

}