方法一：
js:
/**
* 上传图片本地预览方法
* @param {Object} fileObj 上传文件file的id元素 fresh-fileToUpload
* @param {Object} previewObj 预览图片的父层id元素 fresh-send-preview-imgvideo
* @param {Number} maxWidth 预览图最大宽
* @param {Number} minWidth 预览图最小宽
*/
fs.setImagePreview =function(fileObj, previewObj, maxWidth, minWidth) {
var docObj = document.getElementById(fileObj);
var imgObjPreview = document.getElementById(previewObj);
if (docObj.files && docObj.files[0]) {
//火狐下，直接设img属性
//火狐7以上版本不能用上面的getAsDataURL()方式获取，需要一下方式
imgObjPreview.innerHTML ='<img id="fresh-send-preview-img"><i class="fresh-preview-close"></i>';
var img = document.getElementById('fresh-send-preview-img');
img.src = window.URL.createObjectURL(docObj.files[0]);
} else {
//IE下，使用滤镜
try {
var sFilter='filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=scale,src="';
docObj.select();
imgObjPreview.focus();//防止在ie9下拒绝访问，解决办法是让其他的div元素获取焦点
var imgSrc = document.selection.createRange().text;
imgObjPreview.innerHTML ='<img id="fresh-send-preview-img"><i class="fresh-preview-close"></i>';
var img = document.getElementById('fresh-send-preview-img');
img.filters.item('DXImageTransform.Microsoft.AlphaImageLoader').src = imgSrc;
//var rate = (maxWidth/img.height>maxWidth/img.width?maxWidth/img.width:maxHeight/img.height);
//等比例缩放图片的大小
var rate = (img.offsetWidth>maxWidth)?(maxWidth/img.offsetWidth):(img.offsetWidth>minWidth?1:minWidth/img.offsetWidth);
imgObjPreview.innerHTML = "<div id='fresh-send-preview-img' style='width:"+img.offsetWidth*rate+"px;height:"+img.offsetHeight*rate+"px;"+sFilter+imgSrc+"\"'></div><i class='fresh-preview-close'></i>";
} catch (e) {
alert("您上传的图片格式不正确，请重新选择!");
return false;
}
//document.selection.empty();
}
//return true;
}
使用方法：
/**
* 发布新鲜事图片上传方法
* @param {string} dom 任意子节点
*/
fs.fileupload = function(dom) {
var that =$(dom);
if( that.length == 0 ){
return false;
}
if(that.val() == ''){
return false;
}
if (!/\.(gif|jpg|jpeg|png|GIF|JPG|PNG)$/.test(dom.value)) {
alert('图片格式无效！');
return false;
}
//显示图片预览区域
$('#fresh-send-preview').removeClass('hiding');
$('.fresh-send-preview-imgvideo').find('img').attr('src', 'http://img04.xesimg.com/loading.gif');
this.setImagePreview('fresh-fileToUpload', 'fresh-send-preview-imgvideo',120, 36);
};
html:
<div class="fresh-send-preview hide" id="fresh-send-preview">
<div class="fresh-send-preview-imgvideo" id="fresh-send-preview-imgvideo">
<img id="fresh-send-preview-img" src="img/fresh-send-img.png">
<i class="fresh-preview-close"></i>
</div>
</div>
<div class="fresh-send-upload">
<input class="fresh-fileToUpload" id="fresh-fileToUpload" type="file" size="45" name="dynImg" accept="image/*" />
</div>
添加知识点：
如果需要删除预览图片，然后重新上传的话，需要清空file的值，最好的方法是重新赋予相同的file html文件，一边兼容各个浏览器清值的方法不同
//点击关闭图片区域按钮
$('body').off('click', '.fresh-send-box .fresh-preview-close').on('click', '.fresh-send-box .fresh-preview-close', function(){
//删除图片同时清空file的值。以防再次上传同一张图片的时候change不改变无法正常运行
$('.fresh-send-upload').html('<input class="fresh-fileToUpload"
id="fresh-fileToUpload" type="file" size="45" autocomplete="off"
name="dynImg" accept="image/*" />')
$('#fresh-send-preview').addClass('hiding');
});
方法二：
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<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{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='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" border=0 src="head_180.jpg" width="180" height="180" />
</div>
<input type="file" onchange="previewImage(this)" />
</body>
</html>
获取上传图片文件的大小是多少k方法：
var dom = document.getElementById(fileId);//fileId是上传文件的file的id
try {
//非ie9以下的浏览器包括火狐等
console.log(dom.files.item(0).size/1024);
var fileSize = dom.files.item(0).size/1024 +"kB";
} catch (e) {
try {
//ie9以下的浏览器包括ie9
var img = new Image();
img.src = dom.value;
img.onload =function(){
console.log( img.fileSize/1024)
var fileSize = dom.files.item(0).size/1024 +"kB";
}
img.src = dom.value;
} catch (e) {
console.log(23)
return -1;
}
}