为何右侧无输出结果？最后三个函数也不给调用了？
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>返回值函数</title>
<script type="text/javascript">
function app2(x,y)
{ var sum,x,y;
sum = x*y;
return=sum;
}
var req1=app2(5,6), req2=app(2,3);
var sumq=req1+req2;
document.write("req1的值:"+req1+"<br/>");
document.write("req2的值:"+req2+"<br/>");
document.write(req1+"与"+req2+"和:"+sumq);
</script>
</head>
<body>
</body>
</html>
