Javascript - validate form if it is clicked

// Pega o elemento checkbox:
var differentAddress = document.getElementById("differentAddress");

// Pega o elemento que será exibido quando o checkbox for marcado:
var address = document.getElementById("address");

// Exibe ou oculta a parte do formulário quando o checkbox estiver marcado:
differentAddress.onchange = function(event) {
  if (differentAddress.checked) {
    address.style.display = 'block';
  } else {
    address.style.display = 'none';
  }
};

function Validatedatacheckout() {
  var doornumber = document.form.doornumber;
  var road = document.form.road;
  var postcode = document.form.postcode;
  var country = document.form.country;
  var accountnumber = document.form.accountnumber;
  var securitynumber = document.form.securitynumber;

  // Verifica se o checkbox está marcado:
  if (differentAddress.checked) {
    if (doornumber.value == "") {
      window.alert("Please enter a door number.");
      doornumber.focus();
      return false;
    }
    
    if (road.value == "") {
      window.alert("Please enter a road name.");
      road.focus();
      return false;
    }

    if (postcode.value == "") {
      window.alert("Please enter a post code.");
      postcode.focus();
      return false;
    }
    
    if (country.value == "") {
      window.alert("Please enter a country.");
      country.focus();
      return false;
    }
  }

  if (accountnumber.value == "") {
    window.alert("Please enter an account number.");
    accountnumber.focus();
    return false;
  }
  
  if (securitynumber.value == "") {
    window.alert("Please enter a security number.");
    securitynumber.focus();
    return false;
  }
  
  alert("Tudo ok");
}

<form name="form" action="orders.php" method="POST" onsubmit="return Validatedatacheckout()">
  <table id="address" style="display:none">
    <tr>
      <td>
        Door number:<input type="text" placeholder="doornumber" name="doornumber" value="" id="doornumber"> Road:
        <input type="text" placeholder="road" name="road" value="" id="road"> Country:
        <input type="text" placeholder="country" name="country" value="" id="country"> Post Code:<input type="text" placeholder="postcode" name="postcode" value="" id="postcode"> </td>
    </tr>
  </table>
  <label><input name ="differentAddress" id="differentAddress" type='checkbox'>Use a different home address</label>
  <br>
  <br>
  <h5>Please enter your bank details.</h5>
  <div class="form-container">
    <span class="input-label">First Name:</span><input type="text" placeholder="First name" name="firstName"> <br>
    <span class="input-label">Last Name:</span><input type="text" name="lastName" placeholder="Last Name"> <br>
    <span class="input-label">Account Number:</span><input type="text" name="accountnumber" placeholder="account number" onkeypress="return justNumber(event)"> <br>
    <span class="input-label">Security Number:</span><input type="text" name="securitynumber" placeholder="security number" onkeypress="return justNumber(event)">
  </div>
  <br>
  <br>
  <input id="checksub" type="submit" value="Submit">
</form>