alert

Probably the simplest way to see some action from JavaScript is to embed an alert() call in an html file.

examples/js/alert.html
<html>
<head>
    <title>alert example</title>
</head>
<body>
<h1>Welcome to JavaScript</h1>

<script language="javascript">

alert("Hello World");

</script>

More HTML
</body>
</html>