Stay On Current Page, When Form Validation Is False

I want to stay on the current page, if the 'Name' input field is empty. Right now, it shows the error message, and when you click ok, it still goes to the next page (contactcaptcha

Solution 1:

try like so, returning your function at submit event of the form element

<form id="action" action="contactcaptcha.php" method="post" 
 onsubmit="return notEmpty(document.getElementById('Name'), 'Please enter your name')">
    <fieldset>
     ...
     <input type="submit"  name="submit" value="Send your message">    
    </fieldset>
</form>

Solution 2:

Misssing return keyword:

<input type="submit" 
onclick="return notEmpty(document.getElementById('Name'), 'Please enter your name')"   
name="submit" value="Send your message">

Solution 3:

As you use HTML5 anyway, you might want to use the required attribute: http://www.w3schools.com/html5/att_input_required.asp

<form>
  <input id="message" required>
  <input type="submit" value="Submit">
</form>