<script type="text/javascript">

function checkAll(formname, checktoggle)

{

     var checkboxes = new Array();

      checkboxes = document[formname].getElementsByTagName('input');

      for (var i = 0; i < checkboxes.length; i++) {

          if (checkboxes[i].type === 'checkbox') {

               checkboxes[i].checked = checktoggle;

          }

      }

}

</script>



<form name="myform">

<li>

   <label class="cba">

         <a href="javascript:void();" onclick="javascript:checkAll('myform', true);">Check All</a> | 

         <a href="javascript:void();" onclick="javascript:checkAll('myform', false);">UnCheck All</a>

   </label>

</li>

<li>

    <input class="cba" type="checkbox" name="content1" value="1"<?php checked('1', $slct); ?>/>

</li>

<li>

    <input class="cbc" type="checkbox" name="content2" value="2"<?php checked('2', $copy); ?>/>

</li>

<li>

    <input class="cbx" type="checkbox" name="content3" value="3"<?php checked('3', $cut); ?>/>

</li>

</form>

I have made the toggle option for the checkbox check all and uncheck all. Still now check all and uncheck all is not working I get the error in console while viewing in Firebug. Here is the screenshot I attached.
I am not sure what was my mistake:

Any suggestion would be great.