$(document).ready(function(e) { 
    var counter = 0;
    if (window.history && window.history.pushState) {
        $(window).on('popstate', function () {
            window.history.pushState('forward', null, '#');
            //window.location.href="ad.html";   // 回退時跳轉到新頁面
            window.history.forward(1
 
);
            alert("不可回退");
        });
    }

    window.history.pushState('forward', null, '#'); //在IE中必須得有這兩行
    window.history.forward(1);
});