上传之前检测图片大小

<form id="oForm" onsubmit="return CheckFileSize()">
<input type="file" name="oFile" onchange="document.images.oImg.src=this.value"/>
<input type="submit"/>
<img name="oImg" style="position:absolute;top:0;left:0;visibility:hidden"/>
</form>
<script>
function CheckFileSize()
{
if(document.fileSize)
{
 var oImgSize = parseInt(document.images.oImg.fileSize,10)
 alert(oImgSize)
}
else
{
alert("浏览器不支持此功能。")
}
return false
}
</script>