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= '不及格！！';
 }else if (score >=85){
 result="优秀";
 }else
 {
 result="一般般";
 }
}</script>