Jquery ignores response

Hello everyone, why won't my warning work?

 <script type="text/javascript">
 function SubmitForm(method)
 {
  var login = document.form.login.value;
  var password = document.form.password.value;
  $.post("backend.php", { 
                        login: login, 
                        password: password, 
                        method: method},
                        function(data){
                        alert(data.message); 
                        console.log(data.refresh); 
                      }, "json");
            }
   </script>

      

        
        
        
      

    

Response from backend.php

backend{"message":"Log in credentials are not correct","refresh":"false"}