js上传图片前进行预览

<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.style.display = "block";

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>

<style type="text/css">
#preview { overflow:hidden; display:none;}
#imghead { filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=image);}
</style>

<div><input id="fileImg" name="fileImg" onchange="previewImage(this)" type="file" runat="server" /></div>
<div id="preview">
<img id="imghead" width=100 height=100 border=0 src='' />
</div>