JS Multiselect checkbox limit PHP Supported

<script type="text/javascript">

/***********************************************
* Limit number of checked checkboxes script- by JavaScript Kit (www.javascriptkit.com)
* This notice must stay intact for usage
* Visit JavaScript Kit at http://www.javascriptkit.com/ for this script and 100s more
***********************************************/

function checkboxlimit(checkgroup, limit){
    var checkgroup=checkgroup
    var limit=limit
    for (var i=0; i<checkgroup.length; i++){
        checkgroup[i].onclick=function(){
        var checkedcount=0
        for (var i=0; i<checkgroup.length; i++)
            checkedcount+=(checkgroup[i].checked)? 1 : 0
        if (checkedcount>limit){
            alert("You can only select a maximum of "+limit+" checkboxes")
            this.checked=false
            }
        }
    }
}

</script>


<p>Select your favorite two countries below:</p>

<form id="world" name="world">
<input type="checkbox" name="countries[]" /> USA<br />
<input type="checkbox" name="countries[]" /> Canada<br />
<input type="checkbox" name="countries[]" /> Japan<br />
<input type="checkbox" name="countries[]" /> China<br />
<input type="checkbox" name="countries[]" /> France<br />
</form>

<script type="text/javascript">

//Syntax: checkboxlimit(checkbox_reference, limit)
//checkboxlimit(document.forms.world.countries, 2)
checkboxlimit(document.getElementsByName('countries[]'),2); // to support PHP array data
</script>