JavaScriptはページが最後までスクロールすると判断します.

    //    Y       
    function getScrollTop(){
        var scrollTop = 0, bodyScrollTop = 0, documentScrollTop = 0;
        if(document.body){
            bodyScrollTop = document.body.scrollTop;
        }
        if(document.documentElement){
            documentScrollTop = document.documentElement.scrollTop;
        }
        scrollTop = (bodyScrollTop - documentScrollTop > 0) ? bodyScrollTop : documentScrollTop;
        return scrollTop;
    }
    //      
    function getScrollHeight(){
        var scrollHeight = 0, bodyScrollHeight = 0, documentScrollHeight = 0;
        if(document.body){
            bodyScrollHeight = document.body.scrollHeight;
        }
        if(document.documentElement){
            documentScrollHeight = document.documentElement.scrollHeight;
        }
        scrollHeight = (bodyScrollHeight - documentScrollHeight > 0) ? bodyScrollHeight : documentScrollHeight;
        return scrollHeight;
    }
    //        
    function getWindowHeight(){
        var windowHeight = 0;
        if(document.compatMode == "CSS1Compat"){
            windowHeight = document.documentElement.clientHeight;
        }else{
            windowHeight = document.body.clientHeight;
        }
        return windowHeight;
    }
    window.onscroll = function(){
        if(getScrollTop() + getWindowHeight() == getScrollHeight()){
            alert("you are in the bottom!");
        }
    };

$(window).scroll(function(){
　　var scrollTop = $(this).scrollTop();
　　var scrollHeight = $(document).height();
　　var windowHeight = $(this).height();
　　if(scrollTop + windowHeight == scrollHeight){
　　　　alert("you are in the bottom");
　　}
});