js实现input文件上传并在本地实现预览功能-原创手记-慕课网

<title>图片上传本地预览</title>

preview{width:200px;height:190px;border:1px solid #000;overflow:hidden;}

imghead

{width:100%;height:100%;filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=image);display: none}
</style>

    //图片上传预览  IE是用了滤镜。
function previewImage(file)
{
 var MAXWIDTH = 200; 
 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.style.display="block";
   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" src='<%=request.getContextPath()%>/images/defaul.jpg'>
</div>
<input type="file" onchange="previewImage(this)" />
</body>
</html>