Switch condition with checkbox

<script>
function test() {
var cboxes = document.getElementsByName('option_check');
var len = cboxes.length;
for (var i=0; i<len; i++) {
if (cboxes[i].checked){var value=cboxes[i].value;}else{var value='Off';}
alert(value);
}
}
</script>
<input onClick="test()" type="checkbox" value="On" name="option_check">