AJAX I don't receive any response from the server - php

Question

I am using two modals forms in one page, one for login and another for register. From login form you can access the register one. I am trying to show an error based on what I echo without reload the page. Instead of echo I tried to return or print,but I got nothing.I don't receive anything from the server. In console.log show me only "Message".
Here is my code:
register.php
if ($count == 0) {
if ($check == 1)
$query = "INSERT INTO..
elseif ($check == 2)
$query = "INSERT INTO..
else {
$query = "INSERT INTO ..
}
if ($db->query($query)) {
echo "1";
} else {
echo "2";
}
} else {
echo "3";
}
My jS
$("#register").on('submit',function (event) {
event.preventDefault();
/*var $form=$(this);*/
$.ajax({
url : 'register.php',
type : 'POST',
data : $('#id02').serialize(),
success : function (data) {
console.log("Message:"+data);
$('#error-reg').text("Success").css('color', 'green');
},
error: function (msg) {
if(msg=="2") $('#error-reg').html('Error while registering.Please try again');
if(msg=="3") $('#error-reg').html('The username already exists.');
}
});
});

Answer 1

try your error: function with below code to check in details
error: function (xhr, err) {
alert("readyState: "+xhr.readyState+"\nstatus: "+xhr.status);
alert("responseText: "+xhr.responseText);
},

Answer 2

Try This :
success : function (data)
{
if(data==1)
{
$('#error-reg').text("Success").css('color', 'green');
}
else if(data==2)
{
$('#error-reg').html('Error while registering.Please try;
}
else if(data==3)
{
$('#error-reg').html('The username already exists.');
}
}