https://www.jb51.net/article/145157.htm 不支持替换，单张
https://www.cnblogs.com/wangjae/p/11195251.html 支持替换，单张
<!DOCTYPE>
<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 {
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>";
}
}
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" width=100% height=auto border=0 src='a1.png'>
</div>
<input type="file" onchange="previewImage(this)" />
</body>
</html>