Ajax return error Unexpected token < in JSON at position 4

Question

i'm working on a small "facebook like" application for a school project and i'm having some issue with an Ajax request i'm trying to do a like dislike systeme with Jquery Ajax but i got this error in the console when i debug my "data"

Uncaught SyntaxError: Unexpected token < in JSON at position 4

This is my ajax call :

$(document).ready(function(){
$('.like-btn').on('click', function(){
var post_id = $(this).data('id');
$clicked_btn = $(this);
if ($clicked_btn.hasClass('glyphicon glyphicon-thumbs-up')) {
var action = 'like';
} else if($clicked_btn.hasClass('glyphicon glyphicon-thumbs-up liked')){
var action = 'unlike';
}
$.ajax({
type: "POST",
url: 'index.php?action=likes',
data:{
    'action': action,
    'post_id': post_id
},
success: function(data){
    alert("succes");
    console.log(data);
    res = JSON.parse(data);
    if (action == "like") {
        $clicked_btn.removeClass('glyphicon glyphicon-thumbs-up');
        $clicked_btn.addClass('glyphicon glyphicon-thumbs-up liked');
    } else if(action == "unlike") {
        $clicked_btn.removeClass('glyphicon glyphicon-thumbs-up liked');
        $clicked_btn.addClass('glyphicon glyphicon-thumbs-up');
    }
    // Affiche le nombre de like dislike
    $clicked_btn.siblings('span.likes').text(res.likes);
    $clicked_btn.siblings('span.dislikes').text(res.dislikes);

    // Change le style du boutton suivant si user click dessus
    $clicked_btn.siblings('glyphicon glyphicon-thumbs- 
    down').removeClass('glyphicon glyphicon-thumbs- 
    down').addClass('glyphicon glyphicon-thumbs-down disliked');
    }, error: function(jq,status,message) {
    alert('A jQuery error has occurred. Status: ' + status + ' - Message: ' 
    + message);
    console.log(status + message);
    }
    });     

    });

And this is my likes.php :

<?php
function getRating($id)
{
global $pdo;
$rating = array();
$likes_query = "SELECT COUNT(*) FROM rating_info WHERE post_id = ? AND 
rating_action='like'";
$dislikes_query = "SELECT COUNT(*) FROM rating_info 
                WHERE post_id = ? AND rating_action='dislike'";
$likes_rs = $pdo->prepare($likes_query);
$dislikes_rs = $pdo->prepare($dislikes_query);
$likes_rs->execute(array($id));
$dislikes_rs->execute(array($id));
$likes=$likes_rs->fetch();
$dislikes=$dislikes_rs->fetch();
$rating = [
'likes' => $likes[0],
'dislikes' => $dislikes[0]
];
return json_encode($rating);
}



if (isset($_POST['action'])) {
$user_id=$_SESSION['id'];
$return = $_POST;
$post_id = $_POST['post_id'];
$action = $_POST['action'];
switch ($action) {
case 'like':
     $sql="INSERT INTO rating_info (user_id, post_id, rating_action) 
           VALUES ($user_id, $post_id, 'like') 
           ON DUPLICATE KEY UPDATE rating_action='like'";
     break;
case 'dislike':
      $sql="INSERT INTO rating_info (user_id, post_id, rating_action) 
           VALUES ($user_id, $post_id, 'dislike') 
           ON DUPLICATE KEY UPDATE rating_action='dislike'";
     break;
case 'unlike':
      $sql="DELETE FROM rating_info WHERE user_id=$user_id AND 
post_id=$post_id";
      break;
case 'undislike':
      $sql="DELETE FROM rating_info WHERE user_id=$user_id AND 
post_id=$post_id";
  break;
default:
    break;
}


$q = $pdo->prepare($sql);
$q->execute();

echo getRating($post_id);
exit(0);
}

I've tried using datatype:'json' but it also return me an error , Actually it work to insert value in my DB, but it doesnt handle the change of the css and i've got this error. I'm not use to Ajax this might be simple, sorry if i'm saying a stupid question. Thanks you in advance for you time and messages, see ya.

Answer 1

我找到了解决方案，谢谢@ADyson，首先，我已经在自己的文件中更改了php，并且还在php文件中设置了查询参数，所以是的，我认为问题出在我的index.php中，谢谢大家