<input type="checkbox" name="black" />
<input type="checkbox" name="black" />
<input type="checkbox" name="black" />
<input type="checkbox" name="black" />
<input type="checkbox" name="black" />
<input type="checkbox" name="black" />
<input type="checkbox" name="black" />
<input type="checkbox" name="black" />
<input type="checkbox" name="black" />
<script type="text/javascript">
function check(n) {
for (i=0;i<document.getElementsByName("black").length;i++) {
document.getElementsByName("black")[i].checked = i<=n ? true : false;
}
}
for (i=0;i<document.getElementsByName("black").length;i++) {
document.getElementsByName("black")[i].setAttribute("onclick","check("+i+")");
}
</script>