base64显示图片

请选取一个图像文件:

兼容ie的写法 （还没有整理）

 function PreviewImg(el,previewEl,opts){
      this.$el=$(el);
      this.$previewEl=$(previewEl);

      //上传图片触发change事件，改变this指向
      var that=this;
      this.$el.change(function(){
        $.proxy(that.preview(this),that)    
      })


      this.opts=$.extend({},PreviewImg.DEFAULTS,opts)

    }

    //预览图片
    PreviewImg.prototype.preview=function(file){
      var objthis=this;
      var maxWidth  =objthis.opts.maxWidth; 
      var maxHeight = objthis.opts.maxHeight;
      var $previewEl = objthis.$previewEl;
      $previewEl.html('')
      var img = $('#preImg').get(0);
      if (file.files && file.files[0])
      {
        img.onload = function(){
         var rect = objthis._cutImg(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 
     {
      var sFilter='filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=scale,src="';
        file.select();
        var src = document.selection.createRange().text;       
        img.filters.item('DXImageTransform.Microsoft.AlphaImageLoader').src = src;
        var rect = objthis._cutImg(maxWidth, maxHeight, img.offsetWidth, img.offsetHeight);
        $previewEl.html("
");
      }
    }


    //裁剪图片，等比缩放尺寸
    PreviewImg.prototype._cutImg=function(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;
  }


  //默认参数，预览图片的宽高限制
  PreviewImg.DEFAULTS={
    maxHeight:190,
    maxWidth:260
  }