function clacImgZoomParam( maxWidth, maxHeight, width, height ){  //传入四个参数：最大宽度，最大高度，宽度，高度；     var param = { width:width, height:height, top:0, left:0 };      if( width>maxWidth || height>maxHeight ){          rateWidth = width / maxWidth;          rateHeight = height / maxHeight;          if( rateWidth > rateHeight ){              param.width = maxWidth;              param.height = height / rateWidth;          }else{              param.width = width / rateHeight;              param.height = maxHeight;          }      }      param.left = (maxWidth - param.width) / 2;      param.top = (maxHeight - param.height) / 2;      return param;  } 通过这个方法可以很好的判断图片的大小，并以适合的宽高显示在页面中