jquery 判斷網絡圖片，或網絡文件是否存在

$.ajax({
    url : picSrc,
    async : false,
    type : 'HEAD',
    error : function() {
        picSrc　= "https://ss0.bdstatic.com/5aV1bjqh_Q23odCf/static/superman/img/logo_top_ca79a146.png";
    }, success : function() {

    }
});

img.error(function() {
    $(this).attr("src", "https://ss0.bdstatic.com/5aV1bjqh_Q23odCf/static/superman/img/logo_top_ca79a146.png");
});