<!DOCTYPE html>
<html>
<head>
<script>
function myFunction() {
document.getElementById("demo").innerHTML = "Hello World!";
}
</script>
</head>
<body>
<p>When you click "Try it", a function will be called.</p>
<p>The function will display a message.</p>
<button onclick="myFunction()">Try it</button>
<p id="demo"></p>
</body>
</html>