js规定范围内等比控制图片大小

<img src="123.jpg" onload="DrawImage(this,200,200)"/>

function DrawImage(ImgD,FitWidth,FitHeight)
{
   var image=new Image();
   image.src=ImgD.src;
   if(image.width>0 && image.height>0)
   {
     if(image.width/image.height>= FitWidth/FitHeight)
     {
       if(image.width>FitWidth)
       {
         ImgD.width=FitWidth;
         ImgD.height=(image.height*FitWidth)/image.width;
       }
       else
       {
         ImgD.width=image.width;
         ImgD.height=image.height;
       }
     }
     else
     {
       if(image.height>FitHeight)
       {
         ImgD.height=FitHeight;
         ImgD.width=(image.width*FitHeight)/image.height;
       }
       else
       {
          ImgD.width=image.width;
          ImgD.height=image.height;
       }
     }
   }
}