$('document').ready(function () {
                        var get_user = localStorage.getItem("username");
                        var get_pass = localStorage.getItem("password");
                        username = null;
                        password = null;

                        if (get_user != null && get_pass != null) {
                            alert("Tem user: " + get_user + " e password: " + get_pass);
                            username = get_user;
                            password = get_pass;
}

$("#login").click(function (e) {

                            e.preventDefault();
                            if (username == null || password == null) {
                                var username = $("#username").val();
                                var password = $("#password").val();

                                if (username.trim() == '' || password.trim() == '') {
                                    alert("Preenche o campo do utilizador e a password")
                                    return false;
                                }

                            var formData = {
                                'username': username,
                                'password': password,
                            };
                           (data);
                            $.ajax({
                                type: 'POST',
                                url: 'link',
                                data: formData,
                                dataType: 'JSON',
                                success: function (data) {
                                    try {
                                        alert(data[0].username);
                                        alert(data[0].nif);
                                        alert(data[0].datanascimento);
                                        alert(data[0].email);
                                        alert(data[0].contacto);
                                    }
                                    catch (e) {
                                        alert("Utilizador ou password errados.");
                                    }
                                }
                            });

                        },
                        );
                    });