实现代码如下:

function makesmallpic(obj,w,h){
var srcImage = Image;
srcImage.src=obj.src;
var srcW=srcImage.width;
var srcH=srcImage.height;
(srcW>srcH){
(srcW>w){
obj.width=W=w;
obj.height=H=(w/srcW)*srcH;
}{
obj.width=W=srcW;
obj.height=H=srcH;
}
}{
(srcH>h){
obj.height=H=h;
obj.width=W=(h/srcH)*srcW;
}{
obj.width=W=srcW;
obj.height=H=srcH;
}
}
(W>w){
obj.width=w;
obj.height=H*(w/W);
} (H>h){
obj.height=h;
obj.width=W*(h/H);
}
}