为什么我分开赋值没有显示出来，而我直接赋值就可以了呢
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>变量赋值</title>
<script type="text/javascript">
var num1 num2;
num1=10;
num2="JS";
document.write("num1的值是:"+num1);
document.write("num2的值是:"+num2);
</script>
</head>
<body>
</html>
