点击表格行，改变背景颜色

Question

<script type="text/javascript" src="http://code.jquery.com/jquery-latest.js"></script> 
<table id="tt">
<tr><td>aaaaaaaaaaaaaaaaaaaaaaaa</td></tr>
<tr><td>aaaaaaaaaaaaaaaaaaaaaaaa</td></tr>
<tr><td>aaaaaaaaaaaaaaaaaaaaaaaa</td></tr>
<tr><td>aaaaaaaaaaaaaaaaaaaaaaaa</td></tr>
</table>
<script type="text/javascript">
var bat = $();
$("#tt").on("click","tr",function(event){
$(this).css("backgroundColor","#9999ff");
bat.css("backgroundColor","#ffffff");
bat = $(this);
});
</script>