Paste HTML in HTML, JS in the JS pane. Clicks update the preview.

Goal

Count Sell clicks on a Nairobi card.

Paste into the HTML pane:

<p id="out">units 0</p>
<button id="btn" type="button">Sell</button>

Paste into the JS pane:

let n = 0;
document.getElementById("btn").onclick = () => {
  n += 1;
  document.getElementById("out").textContent = "units " + n;
};

document.getElementById("out").textContent = "Nairobi ready";

Another HTML block:

<h1>Mombasa</h1>
<button type="button" id="hi">Greet</button>