Js的三种消息提示窗口

<script type="text/JavaScript">
     alert("我是警告窗口");</script>

<script type="text/JavaScript">
     var res=confirm("确定？");     if (res==true)
     {
         document.write("操作成功");
     }     else
     {
         document.write("操作取消");
     } </script>

<script type="text/JavaScript">function Grades() {
     var score;//分数
     var result;
     score = prompt("Your Grade ?")     if (score < 60){
         result= &#39;不及格！！&#39;;
     }else if (score >=85){
         result="优秀";
     }else
     {
         result="一般般";
     }
}</script>