js上传图片预览的实现方法

本文实例为大家分享了js上传图片预览的方法，供大家参考，具体内容如下

<html >

<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>图片上传本地预览</title>
<style type="text/css">
#preview{width:260px;height:190px;border:1px solid #000;overflow:hidden;}
#imghead {filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=image);}
</style>
<script type="text/javascript">

    //图片上传预览 IE是用了滤镜。
  function previewImage(file)
  {
   var MAXWIDTH = 260;
   var MAXHEIGHT = 180;
   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 //兼容IE
   {
   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;"+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='<%=request.getContextPath()%>/images/defaul.jpg'>
</div>

 <input type="file" onchange="previewImage(this)" />
</body>
</html>

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持我们。