JavaScript判断图片是否存在及加载失败的解决方案

<p>第一种情况：图片存在，正常显示<br />
<img src="https://www.jb51.net/logo.gif"
onerror="javascript:this.src='//www.jb51.net/logos.gif'" /></p>
<p>第二种情况：图片不存在，显示默认图片<br />
<img src="https://www.jb51.net/logoddd.gif"
onerror="javascript:this.src='//www.jb51.net/logos.gif'" /></p>

<script type="text/javascript">
function IsExist(url)
{
x = new ActiveXObject("Microsoft.XMLHTTP")
x.open("HEAD",url,false)
x.send()
return x.status==200
}
alert(IsExist("//www.jb51.net/logos.gif"))
</script>

<SCRIPT language="javascript">
var xmlhttp = new ActiveXObject("Msxml2.XMLHTTP");
xmlhttp.Open("GET", "//www.jb51.net/logos.gif", false);
xmlhttp.Send();
alert(xmlhttp.responseText);
</SCRIPT>

//判断图片是否存在
function checkImgExists(imgurl) {
    var ImgObj = new Image(); //判断图片是否存在
    ImgObj.src = imgurl;
    //存在图片
    if (ImgObj.fileSize > 0 || (ImgObj.width > 0 && ImgObj.height > 0)) {
         return true;
    } else {
         return false;
     }
}