var s="http://www.baidu.com";

var i= s.lastIndexOf("."); //

var unit= s.substring(i); //.com

var url= s.substring(0,i);  //http://www.baidu

   addLoadEvent(func1);

   addLoadEvent(func2);

   function addLoadEvent(func){

       var oldonload=window.onload;

       if(typeof window.onload!='function'){

           window.onload=func;

       }else{

           window.onload=function() {

               oldonload();

               func();

           }

       }

   };

    function func1(){

        alert("text1");

    };

    function func2(){

        alert("text2");

    };

<ul id="imagegallery">

        <li><a href="images/ads/1.jpg" title="广告1">广告1</a></li>

        <li><a href="images/ads/2.jpg" title="广告2">广告2</a></li>

        <li><a href="images/ads/3.jpg" title="广告3">广告3</a></li>

        <li><a href="images/ads/4.jpg" title="广告4">广告4</a></li>

    </ul>

    <p id="description">Choose an image</p>

    <img id="placeholder" src="data:images/ads/adindex.gif" alt="my image gallery">

window.onload = prepareGallery();

    function prepareGallery() {

        if (!document.getElementsByTagName) return false;

        if (!document.getElementById) return false;

        if (!document.getElementById("imagegallery")) return false;

        var gallery = document.getElementById("imagegallery");

        var links = gallery.getElementsByTagName("a");

        for (var i = 0; i < links.length; i++) {

            links[i].onclick = function () {

                return showPic(this) ? false : true;

            }

        }

    }

    function showPic(whichpic) {

        if (!document.getElementById("placeholder")) return false;

        var sourse = whichpic.getAttribute("href");

        var placeholder = document.getElementById("placeholder");

        if (placeholder.nodeName != "IMG") return false;

        placeholder.setAttribute("src", sourse);

        //

        if (document.getElementById("description")) {

            var text = whichpic.getAttribute("title") ? whichpic.getAttribute("title") : "";

            var description = document.getElementById("description");

            if (description.firstChild.nodeType == 3) {

                description.firstChild.nodeValue = text;

            }

        }

        return true;

    }