判斷背景圖片是否加載成功

function loadDefault(){
    var avatar=$("#avatar").css("background-image");
    var imgUrl=avatar.match(/url\("(\S*)"\)/)[1];
    var img=new Image();
    img.src=imgUrl;
    if(img.width==0){
        $("#avatar").css("background-image","url('<%=basePath %>images/mobile/userdefault.png')");
    }else{
        return;
    }
}
window.onload=function(){
loadDefault();
}