手机网页上拉加载内容

$(window).scroll(function() {
    var scrollTop = $(this).scrollTop();
    var scrollHeight = $(document).height();
　　 var windowHeight = $(this).height();
    var positionValue = (scrollTop + windowHeight) - scrollHeight;
    if (positionValue >= 0) {
         //执行ajax，获取数据
    }
});