不会被屏蔽的,只是你弹出了一个,这样焦点就不在body上了,所有后面就没有keyup,可以看下面的代码
<div id="div1">
</div>
<body onkeydown="document.getElementById('div1').innerHTML='aaaa'" onkeyup="alert('u');">
<div id="div1">
</div>
<body onkeydown="document.getElementById('div1').innerHTML='aaaa'" onkeyup="alert('u');">
<head>
<title>Key Event</title>
<script type="text/javascript">
<!--
var strMessage = "";
//-->
</script>
</head>
<body onkeydown="strMessage+='onkeydown\n';" onkeypress="strMessage+='onkeypress\n';" onkeyup="strMessage+='onkeyup';alert(strMessage);strMessage='';">
</body>
</html>
<html>
<head>
<title>Key Event</title>
<script type="text/javascript">
<!--
var strMessage = "";
//-->
</script>
</head>
<body onkeydown="strMessage+=String.fromCharCode(event.keyCode)+' - '+event.keyCode+'\n';strMessage+='onkeydown\n';" onkeypress="strMessage+='onkeypress\n';" onkeyup="strMessage+='onkeyup';alert(strMessage);strMessage='';">
</body>
</html>