title: How can I disable a checkbox after it is checked once?
body: <p>I have created checkboxes which when clicked should call a javacript method.</p>
  
  <pre><code>&lt;input class="checkbox" type="checkbox" name="actor-checkbox" onclick="addTotargetGroup($user);" id=$i &gt;
  </code></pre>
  
  <p>But once the user clicks it, should be disabled and should not allow the users to click it again.</p>