Jquery:float div

111.html

  function Float(elementId,postion,styleCss){  
    this.id = elementId;  
    this.div = $("#"+this.id);  
    this.scrollTop = 0;  
    this.screenHeight = window.screen.height-window.screenTop;  
    this.topPx = rePosition(postion,this);  
    div.css({"position":"absolute","top":topPx+"px"});  
    if(arguments.length > 2)  
        $.each(styleCss,function(i,n){  
            div.css(i,n);  
        });  
    var scrollObj = $.browser.msie ? document.documentElement : document.body;  
    var Expression = null;  
    window.onscroll = function(){  
        this.scrollTop = scrollObj.scrollTop;  
        this.topPx = rePosition(postion,this);  
        div.stop(true).animate({"top":this.topPx},500);  
    }  
}  
function rePosition(postion,obj){  
    switch(postion){  
        case "TOP":  
            obj.topPx = obj.scrollTop;  
            break;  
        case "CENTER":  
            obj.topPx = (obj.scrollTop + ( obj.screenHeight / 2));  
            break;  
        case "BOTTOM":  
            obj.topPx = obj.screenHeight + obj.scrollTop - div.height()-60;  
    }  
    return obj.topPx;  
}  

 //var div = Float("test","CENTER",{"color":"red"});  //使用