function checkFirstName() {
    let regex_firstName = /[A-Z]/;
    var firstName = document.getElementById("firstName");
    var errorMessage = document.getElementById("errorMessage_firstName");
    if (!(regex_firstName.test(firstName.value))) {
        errorMessage.innerHTML = "HALLO!";
        errorMessage.style.display = "block";
     }
     else {
        errorMessage.style.display = "none";
     }

}

function checkLastName() {
    // Erlaubte Zeichen:
    // Großbuchstaben -> [A-Z]
    // Kleinbuchstaben -> [a-z]
    // Bindestrich -> [-]
    // Leerzeichen -> [ ]
    const regex_lastName = /1/;
}

function checkStreetName() {
    // Erlaubte Zeichen:
    // Großbuchstaben -> [A-Z]
    // Kleinbuchstaben -> [a-z]
    // Bindestrich -> [-]
    // 
    const regex_streetName = /1/;
}

function checkHouseNumber() {
    const regex_houseNumber = /1/;
}

function checkPLZ() {
    const regex_plz = /1/;
}

function checkCity() {
    const regex_city = /1/;
}

function checkEmailAddress() {
    const regex_emailAdress = /1/;
}

function checkRepeat_EmailAddress() {
    
}

function checkPassword() {
    const regex_password = /1/;
}

function checkRepeat_Password() {
    // Input des Felds password
    var password = document.getElementById("password");
}