ajax - Verifying if a row already exist in the database

Question

I have a simple form for submitting an email address to a database. I want to check first, using javascript and AJAX, if that email address already exists in the table. The code I am using always returns true regardless if the row already exists in the database. Any hints?

JS Code

<script> 
$('form').submit(function(e) 
{
  alert('submit intercepted');
  e.preventDefault(e);
  var u = $('#email').val();
  $.ajax({
      url: './test2.php',
      type: 'POST',
      data: u,
      success: function (response) {
      //get response from your php page (what you echo or print)
        $('#status').append('<p>The email is ok to use and the row has been inserted </p><p>' + response);
        console.log('Submitted');
      },
      error: function(jqXHR, textStatus, errorThrown) {
        console.log(textStatus, errorThrown);
        alert('Email exists');
      }
    });
});
</script>

HTML Code

<form id="form" action="./test2.php" method="post"> 
    E-mail: <input type="email" name="email" id="email" required><br>
    <span id="status">   </span>
    <input type="submit" id="btnsub">
  </form>

PHP Code

if(isset($email)) {

  $sql_email_check = $conn->query("SELECT Email FROM test WHERE Email='$email' LIMIT 1") ;

  $email_check = $sql_email_check->num_rows;

  if ($email_check < 1) {

    //return "Available";
    return true;   
    //header('Location: /test.php');
    exit();

  } 
  else 
  {
    //return "Unavailable";
    return false;
    //header('Location: /test.php');
    exit(); 

  }
}

Answer 1

So basically the problem was returning the answer from the php code to the ajax function. for some reason the return values were not interpreted correctly as they were expected (from my understanding anyway)

PHP CODE

if(isset($email)) {    
  $sql_email_check = $conn->query("SELECT Email FROM test WHERE Email='$email' LIMIT 1") ;     
  $email_check = $sql_email_check->num_rows;    

  if ($email_check == 0) {
    echo 'true';  
    return; 
    } 
  else 
  {
    echo 'false';
    return;    
  }
}

JS CODE

<script> 
$('form').submit(function(e) 
{
  alert('submit intercepted');
  e.preventDefault(e);
  var u = { 'email': $('#email').val() };
  $.ajax({
      url: 'test2.php',
      type: 'POST',
      //dataType: 'string',
      data: u,
      success: function (response) {
        //get response from your php page (what you echo or print)
        console.log(response);

        if (response === 'true') {
          $('#status').append('<p>The email is ok to use and the row has been inserted </p><p>' + response);

        } else {
          console.log('Email does exist ');

        }
      },
      error: function(jqXHR, textStatus, errorThrown) {
        console.log(textStatus, errorThrown);

      }
    });
});
</script>