JSFiddle - React, Tailwind, and code Playground

HTML

<div id="h1" class="header">Hello </div>
<hr>  
<div id="h2" class="header">what about this one </div>

JavaScript

var header = document.getElementsByClassName('header');
console.log(header);
var newSpan = document.createElement("span");
for(var i=0;i<header.length;i++){
	header[i].appendChild(newSpan);
	newSpan.innerHTML = "i'm here";
}