框架渐显效果

 <script type="text/javascript">
        var Index = {};
        
        Index.DOM = {
            fade:function(obj){
                var DOMObj = document.getElementById(obj);
                if(DOMObj==null||DOMObj == undefined) return;
                var op = Number(DOMObj.getAttribute("opacity"));
                if(Index.Util.isIE()){
                    DOMObj.style.filter="Alpha(opacity="+op+")";
                }else{
                    DOMObj.style.opacity=op/100;
                }
                op = op - 15;
                if(op>0){
                    DOMObj.setAttribute("opacity",op);
                    window.setTimeout("Index.DOM.fade('"+obj+"')",50);    
                }else{
                    DOMObj.removeAttribute("opacity");
                    var overlay = document.getElementById(obj);
                    overlay.parentNode.removeChild(overlay);    
                }
            }
        };
        
        Index.Util = {
            isIE:function(){
                if(window.navigator.appName.indexOf("Internet Explorer")!=-1){
                    return true;
                }else{
                    return false;
                }
            }
        };
        
        
    </script>
<script type="text/javascript">document.write('<div id="iframe_overlay" opacity="100" class="iframe_overlay"><img src="images/loading.gif" align="absmiddle" alt="载入进度" /> 正在载入，请稍候…</div>');
                        </script>
                        <iframe name="iframeLogin" id="iframeLogin" width="100%" frameborder="0" scrolling="No" src="IndexIframeLogin.asp" height="98"></iframe>
                        <script type="text/javascript">
                            var loginIFrame = document.getElementById("iframeLogin"); 
                            loginIFrame.onload = function(){
                                Index.DOM.fade("iframe_overlay");                    
                            }
                        </script>