JSFiddle - React, Tailwind, and code Playground

HTML

<select name="options" id="options">
  <option value="1"> Test1 </option>
  <option value="2">Test2</option>
</select>

<div id="1" class="hidden" style="display: block">Test 1</div>
<div id="2" class="hidden">Test 2</div>

CSS

.hidden 
{
    display: none;   
}

JavaScript

document.getElementById('options').onchange = function()
{
    var i = 1;
    var myDiv = document.getElementById(i);
    while(myDiv) 
    {
        myDiv.style.display = 'none';
        myDiv = document.getElementById(++i);
    }
    document.getElementById(this.value).style.display = 'block';
};