Validation for checkboxes
<p>Hello<br>
I have a JS function which says   </p>

<pre><code>for(var i = 0; i &lt; document.calDailyBlock.selFilCheckBox.length; i++)  
{  
  if(document.calDailyBlock.selFilCheckBox[i].checked)  
  {  
     filteredInitId += document.calDailyBlock.selFilCheckBox[i].value + ",";  
     alert(filteredInitId);  
     isProjCheck = true;  
  }  
}  
document.calDailyBlock.filteredComId.value = filteredInitId;  
</code></pre>

<p>When there are no checkboxes on the page and I try to click on Filter button which calls this function, I receive an error "document.calDailyBlock.selFilCheckBox.length' is null or not an object"  </p>

<p>Is there any simple thing which I can add in this function ?  </p>

<p>Also can anyone help me how to check if there is only one checkbox on one page ?  </p>

<p>Thanks in advance</p>
