<html>
<head>
<script type="text/javascript">
alert(t1);
</script>
<script type="text/javascript">
var t1;
</script>
</head><body>
</body>
</html>为什么不输出"undefined"呢
<html>
<head>
<script type="text/javascript">
alert(t1);
</script>
<script type="text/javascript">
var t1;
</script>
</head><body>
</body>
</html>为什么不输出"undefined"呢
<script type="text/javascript">
//这样就是undefined了
alert(typeof(t1));
</script>