<html>
<head>

<script type="text/javascript">
function myfunction()
{
alert("HELLO")
}
</script>
</head>

<body>
<?php
$txt="Hello World";
echo $txt;
?>
<form>
<input type="button" 
onclick="myfunction()" 
value="Call function">
</form>
<p>By pressing the button, a function will be called. The function will alert a message.</p>

</body>
</html>