<body>
<script>
document.body.onkeydown =function(event){
var e = event || window.event
if(e.keyCode==13)
alert('a')
}
</script>
</body>
<script>
document.body.onkeydown =function(event){
var e = event || window.event
if(e.keyCode==13)
alert('a')
}
</script>
</body>
<script>
document.onkeydown =function(event){
var e = event || window.event
if(e.keyCode==13)
alert('a')
}
</script>
//这个写法可以
<html>
<head>
<title>标题</title>
<script type="text/javascript">
function aalert(e){
var key = window.event?e.keyCode:e.which;
if(key==13)
alert('a');
}
</script>
</head>
<body onkeydown="aalert(event)">
测试
</body>
</html>