title: How to detect that a user has unchecked a checkbox?
body: <p>The following form: </p>
  
  <pre><code>    &lt;form action="x.php" method="get" id="myForm"&gt;Subscribe:
  &lt;div id="radioButtonsWithAdds"&gt;
      &lt;input type="radio" name="group1" value="one"&gt;One month 2,99$  
      &lt;input type="radio" name="group1" value="two"&gt; Two months   5,98$&lt;/div&gt;&lt;br&gt;
      &lt;input type="checkbox" name="option1" value="withAdds" checked&gt;  with adds
      &lt;img src="next.png" border="0" alt="enviar" onclick="document.getElementById('myForm').submit();"&gt; 
      &lt;/form&gt;
  </code></pre>
  
  <p>Is the first part of a subscription from. In here, the user may choose between one month or two months subscription. </p>
  
  <p>If the user agrees to receive adds, leaves the checkbox checked, that will be all, he/she can hit the next button and it's ok. </p>
  
  <p>But if the user unchecks the "with adds" checkbox, a div will show in the place of the #radioButtonsWithAdds one containing another set of radio buttons with different prices. </p>
  
  <p>How can I detect that the checkbox ish without hitting any submit button?</p>