appen_data.js

  <script type="text/javascript">
      $(document).ready(function(){
        var start = 0;
          $.ajax({
              type : "GET",
              url : "get_data.php",
              data : {
                'offset' : 0,
                'limit' : 5
              },
              success: function(data){
                $('.post').append(data);
                start += 5;
              }
          });
          $(window).scroll(function(){
            if($(window).scrollTop() >= $(document).height() - $(window).height()){
              $.ajax({
                  type : "GET",
                  url : "get_data.php",
                  data : {
                    'offset' : start,
                    'limit' : 5
                  },
                  success: function(data){
                    $('.post').append(data);
                    start += 5;
                  }
              });
            }
          });
      });
  </script>