The jquery code:
<script type="text/javascript">
$(function () {
$('.checkall').click(function () {
$('.chk').attr('checked', this.checked);
});
});
</script>
The html:
<input type="checkbox" class="checkall"/> <input type="checkbox" value="1" class="chk"/> <input type="checkbox" value="2" class="chk"/> <input type="checkbox" value="3" class="chk"/> <input type="checkbox" value="4" class="chk"/>