examples/intro/hello_world.html
<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=yes">

  <title>Hello World</title>
</head>
<body>

<button id="go">Say hello</button>

<div id="result"></div>

<script src="hello_world.js"></script>

</body>
</html>
examples/intro/hello_world.js
"use strict";

function greet() {
    document.getElementById('result').innerHTML = 'Hello World';
    return false;
}

document.getElementById('go').addEventListener('click', greet);