求大神们看看为什么无法运行
<!DOCTYPE html>
<html>
<head>
<title> new document </title>
<meta http-equiv="Content-Type" content="text/html; charset=gbk"/>
<script type="text/javascript">
function openWindow(){
var a =confirm("是否打开");
if(a){
var b = prompt("输入要打开的网站","http://www.imooc.com/");
window.open(b,'_blank','width=400,height=500,menubar=no,toolbar=no')
}
}
</script>
</head>
<body>
<input type="button" value="新窗口打开网站" onclick="openWindow()" />
</body>
</html>
