title: Checkbox.checked undefined in OnClick event function
body: <p>With the following code both Javascript functions show the .Checked value is undefined. Anyone know why? I need the cb1 checkbox unset when the cb2 checkbox is set and vice versa.</p>
  
  <pre><code>&lt;html&gt;
    &lt;head&gt;
      &lt;script language="JavaScript" type="text/javascript"&gt; 
  &lt;!--
      function cb2Unset(id){
          box = document.getElementById(id);
          alert(box.Checked);
          if (box.Checked==true){
              testForm.cb2.Checked = false;
          }
      }
  
      function cb1Unset(id){
          box = document.getElementById(id);
          alert(box.Checked);
          if (box.Checked==true){
              testForm.cb1.Checked = false;
          }
      }
  --&gt;
      &lt;/script&gt;
    &lt;/head&gt;
    &lt;body&gt;
      &lt;form method="post" name="testForm"&gt; 
      &lt;input checked="checked" value="1" name="cb1" id="cb1" onclick="cb2Unset(this.id)" type="checkbox"&gt; 
      &lt;input value="1" name="cb2" id="cb2" onclick="cb1Unset(this.id)" type="checkbox"&gt; 
      &lt;/form&gt;
    &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>