JavaScript

var b = isNaN(document.getElementById("txtCoursesTime").value);
        if(b)
        {
            alert("请在课程学时输入数字！");
            return false;
        }

事件：onMouseOver="可以是方法hello()"

target="_blank" 是弹出一个窗口

window.status：状态拦

eg：<a href="a.html" onMouseOver="window.status='这是window窗体的状态拦'"；return true>

求 Session 的剩余时间
<script>
var lefttime=30 //session时间传递
var tid
function x()
{
lefttime--
document.all.xx.innerText="剩余:"+lefttime + "秒"
if(lefttime==0) {clearInterval(tid);window.open("http://dotnet.aspx.cc/")}
}
tid = window.setInterval("x()",1000)
</script>
<body>
<div id=xx></div>

图片缩放:
<script language="JavaScript">
<!--
var flag=false;
function DrawImage(){ ///图片缩放
var ImgD = event.srcElement;
if(ImgD.readyState != "complete") return;
     var image=new Image();
     var my_width;
     var my_height;

my_width = 200;
my_height = 200;

     image.src=ImgD.src;
     if(image.width>0 && image.height>0){
       flag=true;
       if(image.width/image.height>= my_width/my_height){
         if(image.width>my_width){
         ImgD.width=my_width;
         ImgD.height=(image.height*my_width)/image.width;
         }else{
         ImgD.width=image.width;
         ImgD.height=image.height;
         }
         }
       else{
         if(image.height>my_height){
         ImgD.height=my_height;
         ImgD.width=(image.width*my_height)/image.height;
         }else{
         ImgD.width=image.width;
         ImgD.height=image.height;
         }

         }
       }
}
//-->
</script>
</head>
<body>
<img onReadyStateChange="DrawImage()" src="http://www.toodou.com/_upfile/200604041144126360.jpg" />
</body>

AJAX
<script language=javascript>
    var idx = 0 ;
    function ChkSession()
    {
        var Http = new ActiveXObject("Microsoft.XMLHTTP");

       Http.open("GET","test21.aspx",false);

       Http.send();

        var str = Http.responseText;

        if(str=="notnull")
        {
            alert(str);
        }
        else
        {
             alert(str);

             alert("会话值跟踪时间超时,请重新登录...");//这段代码一直没有运行,往下看,你就知道了

        }
        window.setTimeout('ChkSession()', 1000 );//每一秒钟,请求一次test21.aspx
    }
    </script>