JS取得上传图片的大小

<script>
var img=null;
function s()
{
if(img)img.removeNode(true);
img=document.createElement("img");
img.style.position="absolute";
img.style.visibility="hidden";
img.attachEvent("onreadystatechange",orsc);
img.attachEvent("onerror",oe);
document.body.insertAdjacentElement("beforeend",img);
img.src=inp.value;
}
function oe()
{
alert("cant load img");
}
function orsc()
{
if(img.readyState!="complete")return false;
//alert("图片大小："+img.offsetWidth+"X"+img.offsetHeight);
alert("图片尺寸："+img.fileSize);
}
</script>
<input id=inp type="file" onChange="s()">
<br>
<button onclick="s()">Test</button>