Codemirror

index.html

<div id="app"></div>

playground.json

{
  "scripts": [
    "react",
    "react-dom"
  ],
  "styles": [
    "font-awesome"
  ]
}

script.js

function App() {
    return <div>
        <h1>Hi, I'm GistPad teste👋</h1>
        <p>Feel free to edit the HTML, JavaScript and CSS in this playground. The preview will update in real-time, so that you can visually explore your ideas.</p>
        <button onClick={() => alert("Hi!")}>Say Hi <span className="fa fa-heart" /></button>
    </div>;
}

ReactDOM.render(<App />, document.getElementById("app"));

style.css

body {

}