javascript实现缩略图

<script  language="javascript">
//显示缩略图
function DrawImage(ImgD,width_s,height_s){
/*var width_s=139;
var height_s=104;
*/
var image=new Image();
image.src=ImgD.src;
if(image.width>0 && image.height>0){
flag=true;
if(image.width/image.height>=width_s/height_s){
if(image.width>width_s){
ImgD.width=width_s;
ImgD.height=(image.height*width_s)/image.width;
}else{
ImgD.width=image.width;
ImgD.height=image.height;
}
}
else{
if(image.height>height_s){
ImgD.height=height_s;
ImgD.width=(image.width*height_s)/image.height;
}else{
ImgD.width=image.width;
ImgD.height=image.height;
}
}
}
/*else{
ImgD.src="";
ImgD.alt=""
}*/
}
</script>

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