May be its a begginer question but i think i forget something which i cant find because i face such error before where ajax returns html page data instead. but this time I am facing one more issue When i click on button it also return login page below of my current page . Instead of redirecting it login page Open the login page below of current page so without further do here is my code
$(document).on("click","#submit_review",function(e){
e.preventDefault();
var review_comment = $("#review_comment").val();
 var productid = getUrlParameter('id');
    
var reviewarray = [review_comment,productid];
var dataArr = JSON.stringify(reviewarray);    
$.ajax({
        url:"review-ajax.php",
        type:"POST",
        data:{review:dataArr},
        success:function(response){
            alert(response);
            }); 
Here is my ajax code
session_start();
if(isset($_POST['review'])){
    if(isset($_SESSION['email'])){
        
    $json_data = json_decode($_POST['review']);
    $review_comment = htmlspecialchars($json_data[0]);
    $product_id = htmlspecialchars($json_data[1]);        
    $email = $_SESSION['email'];
        
    include "conn.php";    
        
    $useridquery = $con->prepare("SELECT * FROM user WHERE email =:email");    
    $useridquery->bindParam(":email",$email);
    $useridquery->execute();
    $userresult = $useridquery->fetch();   
    $userid = $userresult['id'];
    
    $date = date('d-m-Y');    
        
        
    //Insert in the review table    
    $reviewInsertQuery = $con->prepare("INSERT INTO product_review(product_id, user_id, review_comment,date) VALUES (:product,:user_id,:review,:date)");
    $reviewInsertQuery->bindParam(":product",$product_id);
    $reviewInsertQuery->bindParam(":user_id",$userid);
    $reviewInsertQuery->bindParam(":review",$review_comment);
    $reviewInsertQuery->bindParam(":date",$date);    
    $reviewInsertQuery->execute();        
    
    echo 1; 
        
    }else{
      header('location:loginregister.php'); 
    }
}
   
?>
 
    