图片在未加载完成前显示“加载中...”(图片等比例缩放)

//判断浏览器
var Browser=new Object();
Browser.userAgent=window.navigator.userAgent.toLowerCase();
Browser.ie=/msie/.test(Browser.userAgent);
Browser.Moz=/gecko/.test(Browser.userAgent);

var $=function(id){
    return "string"==typeof(id)?document.getElementById(id):id;
}

//判断是否加载完成
function Imagess(url,imgid,callback,width,height){    
    var val=url;
    var img=new Image();
    if(Browser.ie){
        img.onreadystatechange =function(){  
            if(img.readyState=="complete"||img.readyState=="loaded"){
                callback(img,imgid,width,height);
            }
        }        
    }else if(Browser.Moz){
        img.onload=function(){
            if(img.complete==true){
                callback(img,imgid,width,height);
            }
        }        
    }    
    //如果因为网络或图片的原因发生异常，则显示该图片
    img.onerror=function(){img.src='http://www.baidu.com/img/baidu_logo.gif'}
    img.src=val;
}

//显示图片,按比例缩放显示图片
function checkimg(obj,imgid,width,height){
 var objWidth=obj.width;
 var objHeight=obj.height;
 var ZoomWidth=objWidth;
 var ZoomHeight=objHeight;
 //判断是否超出了规定宽度或高度
 if(width&&height&&objWidth>width||objHeight>height){
     //如果宽度要比长度比例值要大，则要缩减宽度
    if(Math.abs(objWidth-width)>Math.abs(objHeight-height)){
        //高度不变，宽度缩减
        ZoomHeight=objHeight;
        ZoomWidth=(width/height)*objHeight;
        // 裁剪后的宽若还大于规定宽度
        if(ZoomWidth>width){
            ZoomWidth=width;
            ZoomHeight=(height/width)*ZoomWidth;
        }
    }else{//如宽度差小于高度差,则高度裁剪    
        ZoomWidth=objWidth;
        ZoomHeight=(height/width)*objWidth;
        if(ZoomHeight>height){
            ZoomHeight=height;
            ZoomWidth=(width/height)*ZoomHeight;
        }
    }
 }
    $(imgid).src=obj.src;
    $(imgid).style.border="1px solid red";
    $(imgid).style.width=ZoomWidth+"px";//此处一定要加"px"否则ff中不能启作用
    $(imgid).style.height=ZoomHeight+"px";
    if(ZoomWidth<width){
        $(imgid).style.paddingLeft=(width-ZoomWidth)/2+"px";
        $(imgid).style.paddingRight=(width-ZoomWidth)/2+"px";
    }
    if(ZoomHeight<height){
        $(imgid).style.paddingTop=(height-ZoomHeight)/2+"px";
        $(imgid).style.paddingBottom=(height-ZoomHeight)/2+"px";
    }
}
//初始化需要显示的图片，并且指定显示的位置
window.onload=function(){
    Imagess("http://hiphotos.baidu.com/lovebyakuya/pic/item/01cf20088f9506f063d98653.jpg","img1",checkimg,100,100);
    Imagess("http://hiphotos.baidu.com/lovebyakuya/pic/item/7b7b19c70d62f4fdd0006050.jpg","img2",checkimg,100,100);
    Imagess("http://hiphotos.baidu.com/joanne728/pic/item/892557641806d20eaa184c71.jpg","img3",checkimg,100,100);
    Imagess("http://www.neocha.com/-/res/Camilla/20071204181216078845_h.jpg","img4",checkimg,100,100);
    Imagess("http://www.neocha.com/-/res/Camilla/20071204181216d078845_h.","img5",checkimg,100,100);
}
</script>
<img id="img1" src="loading.gif"  />
<img id="img2" src="loading.gif"  />
<img id="img3" src="loading.gif" />
<img id="img4" src="loading.gif" />
<img id="img5" src="loading.gif" />