JSFiddle - React, Tailwind, and code Playground

by Ayri Rin

HTML

<div class="all">
  <p>Выбирай:</p>
   <select onchange="one(this.value)">
      <option>---</option> 
      <option value="1">часть 1</option>
      <option value="2">часть 2</option>
      <option value="3">часть 3</option> 
   </select>
   <div id="one1" style="display:none">
       <p>Текстовка части 1</p>
   </div> 
   <div id="one2" style="display:none">
       <p>Текстовка части 2</p>
   </div>
   <div id="one3" style="display:none">
       <p>Текстовка части 3</p>
   </div>
</div>

CSS

div.all{
  width:100%;
  margin-top:50px;
  text-align:center;
}

JavaScript

function one(m_param){
  m_param = parseInt(m_param);
  for (var i = 1, e; e = document.getElementById('one' + i); ++i)
        e.style.display = i === m_param ? '' : 'none';
}