JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="//cdnjs.cloudflare.com/ajax/libs/font-awesome/4.1.0/css/font-awesome.css">
<iframe name="rte" id="rte" style="border:#000000 1px solid;"></iframe>
<button onclick="makeBold();"><span class="fa fa-bold"></span></button>

JavaScript

var richTextField = document.getElementById("rte");
richTextField.document.designMode = "On";

function makeBold()
{
    richTextField.document.execCommand('bold', false, null);
}