常见JS demo 亲测

<script type=text/javascript src="http://ajax.googleapis.com/ajax/libs/jquery/1.4/jquery.min.js" /></script>

  //google jquery


onclick="event.returnValue=false;"   //禁用checkbox 火狐无效

encodeURIComponent()     JS中文URL编码 utf8

function addFav(t) {document.write('<a href="'+window.location.href+'" title="'+document.title+'" rel="sidebar" onclick="window.external.addFavorite(this.href, this.title);return false;">'+t+'</a>');}
//收藏

<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js"></script>
<script language="JavaScript" type="text/javascript" src="/templets/default/bcc/js/jquery.countdown.min.js"></script>
          <script>
                              var liftoffTime456 = new Date("2011/04/20 11:14:56");
                              var serverdate = new Date("2011/04/21 11:14:56");
                              var localdate = new Date();
                              var jtime = localdate - serverdate;
                             // liftoffTime456.setUTCSeconds(liftoffTime456.getUTCSeconds() + Math.round(jtime / 1000));
                              alert(jtime);
                              $(function() {
                              $('#aa').countdown({ alwaysExpire: true, layout: '{hnn}{sep}{mnn}{sep}{snn}', until: liftoffTime456, format: 'HMS', timezone: +8, onExpiry: function() { liftOff('456') } });
                          });
          </script>
<span id="aa"></span>

   //js 倒计时


    $(function(){
        $('#leftmenu a').click(function(){
            $('#leftmenu a').each(function() {
                $(this).removeClass('tabon');
            });
            $(this).addClass('tabon');
        });
    })
       //li选择器


onclick="document.forms['alipaysubmit'].submit();"
      //图片提交

function ShowPic(file,img,imgname) {
    var fileobj = document.getElementById(file);
    var imgobj = document.getElementById(img);
    fileobj.value = imgname.value;
    if(imgname.files){
         if(imgobj)imgobj.src = imgname.files[0].getAsDataURL();   //火狐
    } else {
        if(imgobj){
            imgobj.style.display = "none";           //IE
            document.getElementById(img+"_div").filters.item("DXImageTransform.Microsoft.AlphaImageLoader").src = imgname.value;
            document.getElementById(img+"_div").filters.item("DXImageTransform.Microsoft.AlphaImageLoader").sizingMethod='scale';
        }
    }
}   


===实例===

<div  id="picnamediv_div" style="FILTER:progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=image);width:160px; height:120px; display:block; overflow:hidden; display:inline; float:left;">
             <?php
          echo eip_image(eip_href_link('upload/none1.png'),'','160','120','id="picnamediv"  name="picnamediv"');
          ?>
</div>




   //上传图片预览      



"星期" + "日一二三四五六".split("")[new Date("2011/2/2").getDay()]
  //JS判断时间


<script language="javascript" type="text/javascript"> 
function DrawImage(ImgD,FitWidth,FitHeight) 
{ 
var image=new Image(); 
image.src="http://java.ccidnet.com/art/3539/20080625/ImgD.src;"  
    if(image.width>0 && image.height>0) 
    { 
        if(image.width/image.height>= FitWidth/FitHeight) { 
            if(image.width>FitWidth) 
            { 
                ImgD.width=FitWidth; 
                ImgD.height=(image.height*FitWidth)/image.width; 
            } 
            else 
            { 
                ImgD.width=image.width; 
                ImgD.height=image.height; 
            } 
        } else { 
            if(image.height>FitHeight) 
            { 
                ImgD.height=FitHeight; 
                ImgD.width=(image.width*FitHeight)/image.height; 
            } 
            else 
            { 
                ImgD.width=image.width; 
                ImgD.height=image.height; 
            } 
        } 
    } 
} 
<script> 


   //缩略图


<script type=text/javascript src="http://ajax.googleapis.com/ajax/libs/jquery/1.4/jquery.min.js" /></script>
<script>
$(function(){
    $("<div>",{
          id: 'test',
          text: 'this is a test',
          "class": "test",
          click: function(){
             $(this).toggleClass('test');
       }
     }).appendTo("body"); 
})
</script> 
   //自动生成

<iframe src="" style="width:800px;height:536px;top:0px;left:0px;position:absolute;visibility:inherit;z-index:-1;" frameborder=0>
</iframe>  

遮挡SELECT
只要在层里面加上下面代码就可以了~
<iframe src="" style="width:800px;height:536px;top:0px;left:0px;position:absolute;visibility:inherit;z-index:-1;" frameborder=0>
</iframe>