用户上传本地磁盘中的一个图片文件作为头像

      //图片上传预览    IE是用了滤镜。

        function previewImage(file)

        {

          var MAXWIDTH  = 180; 

          var MAXHEIGHT = 180;

          var div = document.getElementById(‘preview‘);

          if (file.files && file.files[0])

          {

              div.innerHTML =‘‘;

              var img = document.getElementById(‘imghead‘);

              img.onload = function(){

                var rect = clacImgZoomParam(MAXWIDTH, MAXHEIGHT, img.offsetWidth, img.offsetHeight);

                img.width  =  rect.width;

                img.height =  rect.height;

//                 img.style.marginLeft = rect.left+‘px‘;

                img.style.marginTop = rect.top+‘px‘;

              }

              var reader = new FileReader();

              reader.onload = function(evt){img.src = evt.target.result;}

              reader.readAsDataURL(file.files[0]);

          }

          else //兼容IE

          {

            var sFilter=‘filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=scale,src="http://www.mamicode.com/‘;

            file.select();

            var src = document.selection.createRange().text;

            div.innerHTML = ‘‘;

            var img = document.getElementById(‘imghead‘);

            img.filters.item(‘DXImageTransform.Microsoft.AlphaImageLoader‘).src = src;

            var rect = clacImgZoomParam(MAXWIDTH, MAXHEIGHT, img.offsetWidth, img.offsetHeight);

            status =(‘rect:‘+rect.top+‘,‘+rect.left+‘,‘+rect.width+‘,‘+rect.height);

            div.innerHTML = "

          }

        }

        function clacImgZoomParam( maxWidth, maxHeight, width, height ){

            var param = {top:0, left:0, width:width, height:height};

            if( width>maxWidth || height>maxHeight )

            {

                rateWidth = width / maxWidth;

                rateHeight = height / maxHeight;

                if( rateWidth > rateHeight )

                {

                    param.width =  maxWidth;

                    param.height = Math.round(height / rateWidth);

                }else

                {

                    param.width = Math.round(width / rateHeight);

                    param.height = maxHeight;

                }

            }

            param.left = Math.round((maxWidth - param.width) / 2);

            param.top = Math.round((maxHeight - param.height) / 2);

            return param;

        }