圖片按比例縮放函數_JavaScript

以下是程式碼：

<script language="JavaScript">
<!--
//圖片按比例縮放
var flag=false;
function DrawImage(ImgD,iwidth,iheight){
    //參數(圖片,允許的寬度,允許的高度)
    var image=new Image();
    image.src=ImgD.src;
    if(image.width>0 && image.height>0){
    flag=true;
    if(image.width/image.height>= iwidth/iheight){
        if(image.width>iwidth){  
        ImgD.width=iwidth;
        ImgD.height=(image.height*iwidth)/image.width;
        }else{
        ImgD.width=image.width;  
        ImgD.height=image.height;
        }
        ImgD.alt=image.width+"×"+image.height;
        }
    else{
        if(image.height>iheight){  
        ImgD.height=iheight;
        ImgD.width=(image.width*iheight)/image.height;        
        }else{
        ImgD.width=image.width;  
        ImgD.height=image.height;
        }
        ImgD.alt=image.width+"×"+image.height;
        }
    }
} 
//-->
</script>
調用：<img src="images/toplogo.gif" onload="javascript:DrawImage(this,100,100)">