js 完成对图片的等比例缩放的方法

 /*
     重新按比例设置 页面上对应图片的长和高，
  */
 function resetImgSize(id,imgWidth,imgHeight,posWidth,posHeight) {
     var width = 0;
     var height = 0;
     // 按比例缩小图片的算法
     if(imgWidth > imgHeight) {
         if(imgWidth > posWidth) {
             width = posWidth;
             height = imgHeight/imgWidth * width;

         }else {
             width = imgWidth;
             height = imgHeight;
         }
     }else {
         if(imgHeight > posHeight) {
             height = posHeight;
             width = (imgWidth/imgHeight) * height;
         }else {
             width = imgWidth;
             height = imgHeight;
         }
     }
     width = Math.floor(width);
     height = Math.floor(height);
     $('#'+id).attr('width',width);
     $('#'+id).attr('height',height);
     $('#'+id).css('padding-left',(posWidth-width)/2);
     $('#'+id).css('padding-top',(posHeight-height)/2);

 }

 /*
     获取图片尺寸
     imgURL  图片加载地址
     posId   图片位置id
     posWidth 放在图片位置的width
     posHeight 放在图片位置的height
  */

 function getImgSize(imgURL,posId,posWidth,posHeight) {

     var img = new Image();

     img.src = imgURL+'?'+Math.random();
     var width = 0;
     var height = 0;

     var check = function(){

         if(img.width > 0) {

         clearInterval(set);

         resetImgSize(posId,img.width,img.height,posWidth,posHeight);
         }
     };

     var set = setInterval(check,40);

     img.onload = function(){

         clearInterval(set);
     };

 }

 $(function(){
     $('.resetsize').each(function(){
         getImgSize(this.src,this.id,168,168);
     });
 });