You can refer to Baidu guestbook js_javascript skills

window.onresize = baiduResizeDiv;
window.onerror = function(){}
var divTop,divLeft,divWidth,divHeight,docHeight,docWidth,objTimer,i = 0;
var px = document.doctype?"px":0;
var scrollwidth = navigator.userAgent.indexOf("Firefox")>0?16:0;
var iframeheight = navigator.userAgent.indexOf("MSIE")>0?170-2:209-2;
String.prototype.Trim = function(){return this.replace(/^s |s $/g,"");}
function baidu_collapse(obj){
ct = document.getElementById('tab_c_iframe');
if(ct.style.display=="none"){
ct.style.display="";
obj.src=obj.src.replace("b.gif","a.gif");
} else {
ct.style.display="none";
obj.src=obj.src.replace("a.gif","b.gif");
}
baiduResizeDiv();
}

function baiduMsg()
{
try{
divTop = parseInt(document.getElementById("eMeng").style.top,10);
divLeft = parseInt(document.getElementById("eMeng").style.left,10);
divHeight = parseInt(document.getElementById("eMeng").offsetHeight,10);
divWidth = parseInt(document.getElementById("eMeng").offsetWidth,10);

var scrollPosTop,scrollPosLeft,docWidth,docHeight;
if (typeof window.pageYOffset != 'undefined') {
scrollPosTop = window.pageYOffset;
scrollPosLeft = window.pageXOffset;
docWidth = window.innerWidth;
docHeight = window.innerHeight;
} else if (typeof document.compatMode != 'undefined' && document.compatMode != 'BackCompat') {
scrollPosTop = document.documentElement.scrollTop;
scrollPosLeft = document.documentElement.scrollLeft;
docWidth = document.documentElement.clientWidth;
docHeight = document.documentElement.clientHeight;
} else if (typeof document.body != 'undefined') {
scrollPosTop = document.body.scrollTop;
scrollPosLeft = document.body.scrollLeft;
docWidth = document.body.clientWidth;
docHeight = document.body.clientHeight;
}

document.getElementById("eMeng").style.top = parseInt(scrollPosTop,10) docHeight 10 px;// divHeight
document.getElementById("eMeng").style.left = parseInt(scrollPosLeft,10) docWidth - divWidth - scrollwidth px;
document.getElementById("eMeng").style.visibility="visible";
objTimer = window.setInterval("baidu_move_div()",10);
}catch(e){}
}

function baiduResizeDiv()
{
i =1;
try{
divHeight = parseInt(document.getElementById("eMeng").offsetHeight,10);
divWidth = parseInt(document.getElementById("eMeng").offsetWidth,10);

var scrollPosTop,scrollPosLeft,docWidth,docHeight;
if (typeof window.pageYOffset != 'undefined') {
scrollPosTop = window.pageYOffset;
scrollPosLeft = window.pageXOffset;
docWidth = window.innerWidth;
docHeight = window.innerHeight;
} else if (typeof document.compatMode != 'undefined' && document.compatMode != 'BackCompat') {
scrollPosTop = document.documentElement.scrollTop;
scrollPosLeft = document.documentElement.scrollLeft;
docWidth = document.documentElement.clientWidth;
docHeight = document.documentElement.clientHeight;
} else if (typeof document.body != 'undefined') {
scrollPosTop = document.body.scrollTop;
scrollPosLeft = document.body.scrollLeft;
docWidth = document.body.clientWidth;
docHeight = document.body.clientHeight;
}

document.getElementById("eMeng").style.top = docHeight - divHeight parseInt(scrollPosTop,10) px;
document.getElementById("eMeng").style.left = docWidth - divWidth parseInt(scrollPosLeft,10) - scrollwidth px;
}catch(e){}
}

function baidu_move_div()
{

var scrollPosTop,scrollPosLeft,docWidth,docHeight;
if (typeof window.pageYOffset != 'undefined') {
scrollPosTop = window.pageYOffset;
scrollPosLeft = window.pageXOffset;
docWidth = window.innerWidth;
docHeight = window.innerHeight;
} else if (typeof document.compatMode != 'undefined' && document.compatMode != 'BackCompat') {
scrollPosTop = document.documentElement.scrollTop;
scrollPosLeft = document.documentElement.scrollLeft;
docWidth = document.documentElement.clientWidth;
docHeight = document.documentElement.clientHeight;
} else if (typeof document.body != 'undefined') {
scrollPosTop = document.body.scrollTop;
scrollPosLeft = document.body.scrollLeft;
docWidth = document.body.clientWidth;
docHeight = document.body.clientHeight;
}

try{
if(parseInt(document.getElementById("eMeng").style.top,10) <= (docHeight - divHeight parseInt(scrollPosTop,10)))
{
window.clearInterval(objTimer);objTimer = window.setInterval("baiduResizeDiv()",1);
}
divTop = parseInt(document.getElementById("eMeng").style.top,10);
document.getElementById("eMeng").style.top = divTop - 1 px;
}catch(e){}
}
function baiduMessbox(shape,color,userid){
var styles='position:absolute;top:0px;left:0px;z-index:99999;visibility:hidden;';
var copic='';
if(shape>1) window.onload = baiduMsg;
else {styles='';copic=''}
var s;
if(shape==2) {
s='';
} else if(shape==3) {
s='';
}
document.writeln(s);
}

baiduMessbox(2,1, 849620);