this.userService.registerUser(
        this.registerData.userName,
        () => {
            self.registerData.error = false;
            self.registerData.message = self.registerData.userName + " has been registered";
            self.clearRegisterData();
        })
    }

registerUser = (
        userName: string,
        successCallback) => {   // << What's the type of successCallback ????????

        this.$http({
            method: 'POST',
            url: "/api/Account/Register",
            data: {
                userName: userName,
                firstName: firstName,
                lastName: lastName,
                email: email,
                password: password,
                confirmPassword: confirmPassword
            }
        })
            .success((data) => {
                if (typeof successCallback === 'function') {
                    successCallback(data);
                }
            });
    };