var a="http://www.jb51.net/html/images/logo.gif";
var b=a.split("/");
console.log(b); // ["http:", "", "www.jb51.net", "html", "images", "logo.gif"]
var c=b.slice(b.length-1, b.length).toString(String).split(".");
console.log(c); // ["logo", "gif"]
alert("取得的文件名是:" + c.slice(0, 1)); // 取得的文件名是:logo