为什么这个强制点击广告的代码不行

<table border="0" align="center" cellpadding="0" cellspacing="0">
  <tr>
     <td id="ad_bar" onClick="javascript:hit();">aaa<SCRIPT language=JavaScript src="csdn_ggmm.js" type=text/javascript></SCRIPT></td>
  </tr>
  <tr>
     <td height="25" align="center"><a href="javascript:to_read();" id="go_read" target="_blank">我要阅读</a></td>
  </tr>
</table>
</div>
<script language="JavaScript" type="text/javascript">
function hit(){
go_read.href="ww.htm";
alert(go_read.href)
}
function to_read(){
alert("请先点击上面的广告");
ad_bar.focus();
}
</script>