I don't accept the naysayers' answers.
If you find some special package that makes it work, then you can do it yourself! So, I don't buy those answers.
onClick is a kludge that involves the end-user, hence not acceptable.
@umesh came close, but it was not a standalone program. Here is such (adapted from his Answer):
<script type="text/javascript">
function JSFunction() {
alert('In test Function'); // This demonstrates that the function was called
}
</script>
<?php
// Call a JS function "from" php
if (true) { // This if() is to point out that you might
// want to call JSFunction conditionally
// An echo like this is how you implant the 'call' in a way
// that it will be invoked in the client.
echo '<script type="text/javascript">
JSFunction();
</script>';
}