Can't get form to show on button click PHP/Javascript

I can't get the form to show when the button is clicked, any ideas? I have included the js file in the header.

myfile.php

 
$commentid = $commentdata['ID'];
echo '<input type="button" value="';
echo _('Reply');
echo '" onclick="comNew(';
echo "'".$commentdata['ID']."'";
echo ')"/>';
echo '<div id="comForm'.$commentid.'"></div>';

PHP:

doit.js

function comNew(parentId)
{
	$.post("createComment.php",{pid:parentId},
	function(data)
	{
		$('ComNew' + parentId).html(data);
	});
}

Code (markup):

createComment.php

<?php
include("db.php");
$parentid = $_POST['pid'];
?>
<form action="#" method="post">
<input type="hidden" name="childcom" value="Y">
<input type="hidden" name="childcomid" value="<?php echo $parentid; ?>">
<textarea rows="10" cols="50" name="content" /><br />
<input type="submit" value="Submit" />
</form>

PHP:

Thanks for any help!

 

Nevermind, it was easier to do like this

echo '<input type="button" value="';
			echo _('Reply');
			echo '" onclick="reply(';
			echo "'".$commentdata['ID']."'";
			echo ');"/>';
			echo '<div id="'.$commentid.'" style="display: none;">';
			?>
			<form action="#" method="post">
			<input type="hidden" name="childcom" value="Y">
			<input type="hidden" name="childcomid" value="<?php echo $commentid; ?>">
			<textarea rows="10" cols="50" name="content" /></textarea><br />
			<input type="submit" value="Submit" />
			</form>
			<?php
			echo '</div>';

PHP:

<script>
    function reply(id) {
        var state = document.getElementById(id).style.display;
            if (state == 'block') {
                document.getElementById(id).style.display = 'none';
            } else {
                document.getElementById(id).style.display = 'block';
            }
        }
</script>

Code (markup):