function checkForm() {
    errMessage = "";

    if (!IsZipcode(document.getElementById('customer_address_zip_input').value)) {
        errMessage += "Please enter a valid zip code.\n";
    }

    if(errMessage != "") {
        errMessage = "Please Fix the following Field(s):\n\n" + errMessage;
        alert(errMessage); 
        return false; 
    } 
    
    return true; 
}