JSFiddle - React, Tailwind, and code Playground

HTML

<div class="testClass">
	A div with class="testClass".
</div>
<div class="testClass">
	The second div with the same class name.
</div>
<p class="testClass">
	A paragraph with testClass
</p>

<button onclick="testFunction();">Alert the content of the first testClass</button>

<script>
function testFunction() {
    var x = document.getElementsByClassName("testClass");
    alert(x[0].innerHTML);
}
</script>