javascript简单实现等比例缩小图片的方法

//等比例缩小图片
function changeImg(obj,width,height) {
  var img = new Image();
  img.src = document.getElementById(obj.id).src
  var ys_w = img.width;
  var ys_h = img.height;
  if(ys_w > width || ys_h > height)
  {
    var scale;
    var scale1 = ys_w / width;
    var scale2 = ys_h / height;
    //alert(scale1+","+scale2);
    if(scale1 > scale2)
    {
      scale = scale1;
    }
    else
    {
      scale = scale2;
    }
    document.getElementById(obj.id).style.width = ys_w / scale;
    document.getElementById(obj.id).style.height = ys_h / scale;
  }
}