纯JS实现图片上传和预览

<script type="text/javascript">
function previewImage(file) {
var MAXWIDTH = 150;
var MAXHEIGHT = 200;
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 {
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;margin-left:" + rect.left + "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>

<div style="display: none">
<asp:FileUpload ID="FupImg" onchange="previewImage(this)" runat="server"></asp:FileUpload>
</div>
<a href="Javascript:void()" onclick="FupImg.click()">
<div id="preview">
<asp:Image ID="ImgTx" ImageUrl="/Images/1111.jpg" runat="server" /></div>
</a>