jQuery 全选 正反选

<script src="http://code.jquery.com/jquery-1.4.4.min.js" type="text/javascript"></script>
<script type="text/javascript">
$(function() {

$('input').attr("checked",true); 
$("#checkAll").click(function() {
$('input[name="subBox"]').attr("checked",this.checked);
});
var $subBox = $("input[name='subBox']");
$subBox.click(function(){
$("#checkAll").attr("checked",$subBox.length == $("input[name='subBox']:checked").length ? true : false);
});
});
</script>

<div>
<input id="checkAll" type="checkbox" />全选
<input name="subBox" type="checkbox" />项1
<input name="subBox" type="checkbox" />项2
<input name="subBox" type="checkbox" />项3
<input name="subBox" type="checkbox" />项4
</div>

默认全部选中