哪里错了？
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>window对象</title>
<script type="text/javascript">
function wopen(){
alert("欢迎来到慕课网！");
var satrt=confirm("是否打开慕课网？");
if(start==true){
window.open('http://www.imooc.com','_blank','width=600 height=400');
}
else{
alert("再见!");
}
}
</script>
</head>
<body>
<form>
<input type="button" value="点击我，打开新窗口" onclick="wopen()" />
</form>
</body>
</html>
