javascript check all and uncheck

<script language='javascript'>
function toggleAll(cb)
{
    var val = cb.checked;
    var frm = document.forms[0];
    var len = frm.elements.length;
    var i=0;
    for( i=0 ; i<len ; i++)
    {
        if (frm.elements[i].type=="checkbox" && frm.elements[i]!=cb)
        {
            frm.elements[i].checked=val;
        }
    }
}
</script>
//Sample Usage
<form >
Check ALL
<input type="checkbox" name="checkall" onclick="toggleAll(this)" id="Checkbox1" />
<br>
<input type="checkbox" name="check1" id="Checkbox2" />
<input type="checkbox" name="check2" id="Checkbox3" />
<input type="checkbox" name="check3" id="Checkbox4" />
<input type="checkbox" name="check4" id="Checkbox5" />
<input type="checkbox" name="check5" id="Checkbox6" />
</form>