Ajax Post请求不起作用

Question

Hello I have created a script for login using ajax method I tried but this is not working for me getting unsuccessful can you please let me know why i am unable to work with this

function login() {
var username = document.getElementById('username').value;
var pass     = document.getElementById('pass').value;

if(username == '' && pass == '') {
    alert('Fields could not be left empty');
} else {
    $.ajax({
        type     : "POST",
        url      : "includes/register.php",
        data     : "command=login&username="+username+"&password="+pass,
        datatype : "json",
        success  :  function(data) {
            if (data.status == 200) {
                alert('Successfull');
                var return_data = data.responseText;
                document.getElementById('messagearea').innerHTML = return_data;
            } else {
                alert('Unsuccessful');
            }
        }
    });
}
}

it should run alert successful but I am getting alert('Unsuccessful') it means that status is not equal 200 can anyone help me out with that

Here is my php code

if(isset($_POST['command']) && $_POST['command'] == 'login') {
    $username = $_POST['username'];
    $pass     = $_POST['pass'];
    $password = md5($pass);

    $check  = mysqli_query($connection, "SELECT * FROM users WHERE username = '$username'");
    $result = mysqli_num_rows($check);
    if($result != 1) {
        echo "<div class='message'>Response Successful</div>";
    } else {
        echo "<div class='message'>Username/Password did not matched</div>";
    }
}

Answer 1

T in datatype should be capital,

$.ajax({
      type: "POST",
      url: "includes/register.php",
      data: "command=login&username=" + username + "&password=" + pass,
      dataType: "json",

As per the server code, your data should be look like this

data: "command=login&username=" + username + "&pass=" + pass,

change the code inside the success handler like this,

document.getElementById('messagearea').innerHTML = data;