JSFiddle - React, Tailwind, and code Playground

HTML

<div id="testel">
<span class="span1">This is a span</span>
<input type="button" onclick="testFunc();" value="Test">
</div>

CSS

.span1 {
  color:red;
  
}

JavaScript

function testFunc() {
 var el = document.getElementById("testel");
 var ch = getElementByClass(el,"span1");
 alert('Hello');
 
 }
 
 function getElementByClass(elparent,class) {
 for (var i = 0; i < elparent.childNodes.length; i++) {
    if (elparent.childNodes[i].className == class) {
      return elparent.childNodes[i];
      break;
    }
 }
 }