为什么新窗口中的网址自动添加了当前页面地址
<script type="text/javascript">
function openWindow(){
var d = confirm("打开新窗口吗？");
if(d==true){
var url = prompt("输入网址：","http：//www.imooc.com/");
if(url!=null){
window.open(url,"_blank","width=400,height=500,menubar=on,toolbar=on");
}
}
}
</script>
