js 图片上传本地预览

<!doctype html>
<html lang="en">
<head>
<meta 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='"+rect.width+"px;height:"+rect.height+"px;margin-top:"+rect.top+"px;"+sFilter+src+""'></div>";
            div.innerHTML = "<div id=divhead style='"+rect.width+"px;height:"+rect.height+"px;"+sFilter+src+""'></div>";
        }
    }

    function clacImgZoomParam( maxWidth, maxHeight, width, height ){
        var param = {top:0, left:0, 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" border="0" src="head_180.jpg" width="180" height="180" />
</div>
<input type="file" onchange="previewImage(this)" />
   
</body>     
</html>
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