上传图片预览

<! 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 >
< title > Firefox3,IE6,IE7,IE8上传图片预览</ title >
< meta http-equiv ="Content-Type" content ="text/html; charset=utf-8" />

< style type ="text/css" >
#preview_wrapper {
display : inline-block ;
width : 300px ;
height : 300px ;
background-color : #CCC ;
}
#preview_fake { /* 该对象用户在IE下显示预览图片 */
filter : progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=scale) ;
}
#preview_size_fake { /* 该对象只用来在IE下获得图片的原始尺寸，无其它用途 */
filter : progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=image) ;
visibility : hidden ;
}
#preview { /* 该对象用户在FF下显示预览图片 */
width : 300px ;
height : 300px ;
}
</ style >


< script type ="text/javascript" >
function onUploadImgChange(sender){
if ( ! sender.value.match( / .jpg|.gif|.png|.bmp / i ) ){
alert( ' 图片格式无效！ ' );
return false ;
}
var objPreview = document.getElementById( ' preview ' );
var objPreviewFake = document.getElementById( ' preview_fake ' );
var objPreviewSizeFake = document.getElementById( ' preview_size_fake ' );
if ( sender.files && sender.files[ 0 ] ){
objPreview.style.display = ' block ' ;
objPreview.style.width = ' auto ' ;
objPreview.style.height = ' auto ' ;
// Firefox 因安全性问题已无法直接通过 input[file].value 获取完整的文件路径
objPreview.src = sender.files[ 0 ].getAsDataURL();
} else if ( objPreviewFake.filters ){
// IE7,IE8 在设置本地图片地址为 img.src 时出现莫名其妙的后果
// （相同环境有时能显示，有时不显示），因此只能用滤镜来解决
// IE7, IE8因安全性问题已无法直接通过 input[file].value 获取完整的文件路径
sender.select();
var imgSrc = document.selection.createRange().text;
objPreviewFake.filters.item( ' DXImageTransform.Microsoft.AlphaImageLoader ' ).src = imgSrc;
objPreviewSizeFake.filters.item( ' DXImageTransform.Microsoft.AlphaImageLoader ' ).src = imgSrc;
autoSizePreview( objPreviewFake, objPreviewSizeFake.offsetWidth, objPreviewSizeFake.offsetHeight );
objPreview.style.display = ' none ' ;
}
}

function onPreviewLoad(sender){
alert( ' onload ' );
autoSizePreview( sender, sender.offsetWidth, sender.offsetHeight );
}

function autoSizePreview( objPre, originalWidth, originalHeight ){
var zoomParam = clacImgZoomParam( 300 , 300 , originalWidth, originalHeight );
objPre.style.width = zoomParam.width + ' px ' ;
objPre.style.height = zoomParam.height + ' px ' ;
objPre.style.marginTop = zoomParam.top + ' px ' ;
objPre.style.marginLeft = zoomParam.left + ' px ' ;
}

function clacImgZoomParam( maxWidth, maxHeight, width, height ){
var param = { width:width, height:height, top: 0 , left: 0 };
if ( width > maxWidth || height > maxHeight ){
rateWidth = width / maxWidth;
rateHeight = height / maxHeight;
if ( rateWidth > rateHeight ){
param.width = maxWidth;
param.height = height / rateWidth;
} else {
param.width = width / rateHeight;
param.height = maxHeight;
}
}
param.left = (maxWidth - param.width) / 2;
param.top = (maxHeight - param.height) / 2;
return param;
}

</ script >

</ head >


< body >
< div id ="preview_wrapper" >
< div id ="preview_fake" >
< img id ="preview" onload ="onPreviewLoad(this)" />
</ div >
</ div >
< br />
< input id ="upload_img" type ="file" onchange ="onUploadImgChange(this)" />< br />
< img id ="preview_size_fake" />

</ body >

</ html >