即使成功，Ajax也会触发错误

Question

这是我第一次将Ajax与PHP结合使用，而且我很难将其付诸实践。

我有这段Ajax代码：

$.ajax({
            url:  '/dev/php/login.php',
            type: 'POST',
            dataType: 'json',
            error: function(date) {
                console.log(date);
                alert("Het emailadres of wachtwoord is onjuist");
            },
            data: {email:email,password:password},
            success: function(response) {
                console.log(response);
                alert(response);
            }
        })

使用此PHP代码：

<?php
$servername = "blur";
$username = "blur";
$dbpassword = "blur";
$dbname = "blur";

$emailadres = $_POST['email'];
$password = $_POST['password'];
// Create connection

$conn = new mysqli($servername, $username, $dbpassword, $dbname);

// Check connection
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
} 
$encodedpass = md5($password);

$sql = "SELECT first_name, last_name FROM account WHERE `email`='$emailadres' AND `password`='$encodedpass'";
$result = $conn->query($sql);

if ($result->num_rows > 0) {
    // output data of each row
    while($row = $result->fetch_assoc()) {
        echo "Name: " . $row["first_name"]. " " . $row["last_name"] . " WEEEE";
    }
}

else {
if (!function_exists('http_response_code'))
{
    function http_response_code($newcode = NULL)
    {
        static $code = 200;
        if($newcode !== NULL)
        {
            header('X-PHP-Response-Code: '.$newcode, true, $newcode);
            if(!headers_sent())
                $code = $newcode;
        }       
        return $code;
    }
}
}
$conn->close();
?>

由于某种原因，Ajax中的错误函数总是被调用，即使响应文本回应了数据库中的名称。它看起来像这样：