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兼容好的JS图片上传预览代码

  • 标签:图片预览 更新时间:2014-04-06
  • 在上传图片前预览图片的功能,可提高你网站的用户体验,让用户清楚所要上传的图片是不是选对了。本代码无JS插件,纯JavaScript结合HTML来实现,是一个很不错的例子,比较完整:

    <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
    <html xmlns="http://www.w3.org/1999/xhtml" >
    <head>
    <title>本地图片预览</title>
    <style type="text/css">
    #preview{width:100px;height:100px;border:1px solid #000;overflow:hidden;}
    #imghead {filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=image);}
    </style>
    <script type="text/javascript">
    function previewImage(file)
    {
      var MAXWIDTH  = 100;
      var MAXHEIGHT = 100;
      var div = document.getElementById('preview');
      if (file.files && file.files[0])
      {
        div.innerHTML = '<img id=imghead>';
        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
      {
        var sFilter='filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=scale,src="';
        file.select();
        var src = document.selection.createRange().text;
        div.innerHTML = '<img id=imghead>';
        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 = "<div id=divhead style='width:"+rect.width+"px;height:"+rect.height+"px;margin-top:"+rect.top+"px;margin-left:"+rect.left+"px;"+sFilter+src+"\"'></div>";
      }
    }
    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;
    }
    </script>
    </head>
    <body>
    <div id="preview">
        <img id="imghead" width="100" height="100" border="0" src='../images/demo.jpg'><!--无预览时的默认图像,自己弄一个-->
    </div>
        <br/>
        <input type="file" onchange="previewImage(this)" />
    </body>
    </html>
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