<html>
<head>
  <meta charset="utf-8">
  <title>Counter</title>
</head>
<body>
  <script src="https://unpkg.com/apprun/dist/apprun-html.js"></script>
  <script>
    const state = 0;
    const view = state => {
      return `<div>
        <h1>${state}</h1>
        <button onclick='app.run("-1")'>-1</button>
        <button onclick='app.run("+1")'>+1</button>
      </div>`;
    };
    const update = {
      '+1': state => state + 1,
      '-1': state => state - 1
    };
    app.start(document.body, state, view, update);
  </script>
</body>
</html>