JavaScript实现图片按比例自动缩放

/**
 * 限制图片显示的size.
 * 
 * @param thisobj 图片组件
 * @param limitW 限制宽度大小
 * @param limitH 限制高度大小
 */
function imageResize(thisobj, limitW, limitH) {
  var newW;
  var newH;
  if (thisobj.width > limitW) {
    newW = limitW;
    newH = parseInt(thisobj.height * newW / thisobj.width);
 // 按宽度比例缩放
    if (newH > limitH) {
      newH = limitH;
      newW = parseInt(thisobj.width * newH / thisobj.height);
    }
    thisobj.width = newW;
    thisobj.height = newH;
  } else if (thisobj.height > limitH) {
    newH = limitH;
    newW = parseInt(thisobj.width * newH / thisobj.height);
    thisobj.width = newW;
    thisobj.height = newH;
  }
}