javascript图片按比例缩放

<!--
//图片按比例缩放
var flag=false;
function  FormatImage(ImgD,iwidth,iheight){
    //参数(图片,允许的宽度,允许的高度)
    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;
        }
        }
     else{
        if(image.height>iheight){  
        ImgD.height=iheight;
        ImgD.width=(image.width*iheight)/image.height;        
        }else{
        ImgD.width=image.width;  
        ImgD.height=image.height;
        }
        }
    }
} 

//-->