var login = prompt("请输入登录邮箱");

    function file() {

        var Username = login.indexOf("@");

        return login.slice(0,Username);

    }

    function next() {

        var domianName = login.indexOf("@");

        return login.slice(domianName+1)

    }

    var first = file(login);

    document.write("邮箱的用户名是:" + first + "<br/>");

    var second = next(login);

    document.write("登陆邮箱的域名是:" + second+"邮箱");