js验证上传图片大小和格式

function validatePicture(obj)
{
var boolResult = true;
var imgUrlLength = obj.value.length;
if(imgUrlLength != 0)
{
var imgUrl = obj.value.toLowerCase();
var imgUrlType = imgUrl.substring(imgUrlLength-4,imgUrlLength);
if(imgUrlType != ".jpg" && imgUrlType != ".gif")
{
alert("上传文件格式不正确！");
obj.outerHTML = obj.outerHTML;
boolResult = false;
}
else
{
var myImg = new Image();
myImg.src = obj.value;
myImg.onreadystatechange = function ()
{
if(myImg.readyState == "complete")
{
var fs = myImg.fileSize;
if(fs > 1024*50) //50KB
{
alert("上传图片不能超过50KB！");
obj.outerHTML = obj.outerHTML;
boolResult = false;
}
}
}
}
}
return boolResult;
}

使用时直接 onchange validatePicture(this)就可以了