For example:

<script type="text/javascript">
<!--
alert('Test');
//-->
</script>

However if you are using this trick with the initialization parameter facelets.SKIP_COMMENTS set to true, the code between <!-- and //--> won’t even be sent to the client!
It simply means that the code above won’t open an alert window because it has been skipped during the page rendering.

Here is what the client will receive:

<script type="text/javascript">
<!--
//-->
</script>

You have two solutions to avoid this situation:

1. Set the SKIP_COMMENTS parameter to false (the default is true). This can’t really hurt, your page will just be heavier depending on how much HTML comments you put on your page;
2. No need to hide the JavaScript code as all browsers are now supporting it and over 99.9% of users have it enabled – this is the solution I chose.

For information, below is the code to put in your web.xml file to set the SKIP_COMMENTS parameter to false:

<context-param>
    <param-name>facelets.SKIP_COMMENTS</param-name>
    <param-value>false</param-value>
</context-param>