为什么出现网页丢失？
<!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("open?");
if(a==true){
var b=prompt("输入网址","http：//www.imooc.com");
if(b!=null){
window.open('b','width=400,height=500,menubar=no,toolbar=no')
}
else{alert("bye");}
}
else{alert("bye");}
}
</script>
</head>
<body>
<input type="button" value="新窗口打开网站" onclick="openWindow()" />
</body>
</html>
