งงว่าทำไมแทรก code ตรงนี้แล้ว error เลยทันทีครับ JSON

<?php
if(isset($_POST['task']) && $_POST['task'] == 'comment_insert')
{
	$userId = (int)$_POST['userId'];
	$comment = addslashes(str_replace( "\n" , "<br>", $_POST['comment'])); 

	$std = new stdClass(); 
	$std->comment_id = 24;
	$std->userId = $userId;
	$std->comment = $comment;
	$std->userName = "Supanat";
	$std->profile_img = "http://s3.amazonaws.com/37assets/svn/765-default-avatar.png";

	require_once '../mysql/models/comments.php'; 
	if(class_exists('Comments'))
	{
		$commentInfo = Comments::insert( $comment, $userId); //$comment จากข้างบนตรง addslash
		if($commentInfo != null)
		{

		}
	}

	echo json_encode($std);

}
else
{
	header('location: /');  //go to main page use slash
}
?>

<?php

class Comments
{
	public static function getComments()
	{

	}

	public static function insert($commentText, $userId)  //although insert to db but also return a stdClass Object from the database
	{


		$std = new stdClass(); //stdClass is a empty class that is already in PHP system
		$std->comment_id = null;  //name from variable in db
		$std->comment = $comment_txt;
		$std->userId = (int)$userId;

		return $std;
	}

	public static function update($data)
	{

	}

	public static function delete($commentId)
	{
		//delete the comment from the comment database using the id of comment_id
	}
}

?>

$(document).ready(function(){
	$('#post-btn').click(function(){
		comment_post_btn_click(); //เรียกใช้ function
	});	
});



function comment_post_btn_click()
	{
		var text = $('#posttext').val(); //get value from text
		var userid = $('#user-id').val();
		var user_name = $('#user-name').val();

		if(text.length > 0 && userid != null)
		{
			
			$('.comment-insert-container').css('border', '1px solid #e1e1e1');  //after border red from emptypost so then if notempty post oldcolor will be back

			$.ajax({  
				type: "POST",
				url: "ajax/comment_insert.php",
				data: {
					task : "comment_insert",
					userId : "userid",
					comment : text 
				},
				success : function(data)
				{
					comment_insert( jQuery.parseJSON(data));
					console.log("ResponseText " + data);
				},
				//dataType: 'html' //not neccessary
			});

			

			console.log(text + " Username: " + user_name + " User ID: " + userid );
		}
		else
		{
			//text empty and then let's put a border of red on it
			$('.comment-insert-container').css('border', '1px solid red');
			console.log("The text was empty");
		}

		
		$('#posttext').val(""); 
	}

	function comment_insert(data)
	{
		var t = '';
		t += '<li class="comment-holder" id="_'+data.comment_id+'">';   //copy from foler include/commentbox.php
		t += '<div class="user-img">';
		t += '<img src="'+data.profile_img+'" class="user-img-pic" />';
		t += '</div> ';
		t += '<div class="comment-body">';
		t += '<h3 class="username-field">'+data.userName+'</h3>';
		t += '<div class="comment-text">'+data.comment+'</div>';
		t += '</div>';
		t += '<div class="comment-button-holder">';
		t += '<ul>';
		t += '<li class="delete-btn">X</li>';
		t += '</ul>';
		t += '</div>';
		t += '</li>';
							
		$('.comment-holder-ul').prepend( t );
	}