Infinite Scrolling UserScript?

infiniteScrolling.user.js

// ==UserScript==
// @name         Gist Infinite Scroll
// @namespace    https://gist.github.com/*
// @version      0.1
// @description  Infinite Scroll on github gists
// @author       Jason McElhenney
// @match        http://gist.github.com/*  // Adjust this to match the websites you want the script to run on
// @grant        GM_xmlhttpRequest
// @grant        unsafeWindow
// @require      https://code.jquery.com/jquery-3.6.0.min.js
// ==/UserScript==

(function() {
    'use strict';
    
    // js file

    var next_data_url; // replaced when loading more
    var prev_data_url; // replaced when loading more
    var next_data_cache;
    var prev_data_cache;
    var last_scroll = 0;
    var is_loading = 0; // simple lock to prevent loading when loading
    var hide_on_load = false; // ID that can be hidden when content has been loaded

    function loadFollowing() {
      if (next_data_url=="") {
        $('div.pagination').show();
      } else {
        is_loading = 1; // note: this will break when the server doesn't respond
        $('div.pagination').hide();

        function showFollowing(data) {
          $('div.listitempage:last').after(data.response);
          next_data_url = data.next_data_url;
          next_data_cache = false;
          $.getJSON(next_data_url, function(preview_data) {
            next_data_cache = preview_data;
          });
        }
        if (next_data_cache) {
          showFollowing(next_data_cache);
          is_loading = 0;
        } else {
          $.getJSON(next_data_url, function(data) {
            showFollowing(data);
            is_loading = 0;
          });
        }
      }
    };

    function loadPrevious() {
      if (prev_data_url=="") {
        $('div.pagination').show();
      } else {
        is_loading = 1; // note: this will break when the server doesn't respond
        $('div.pagination').hide();

        function showPrevious(data) {
          $('div.listitempage:first').before(data.response);
          item_height = $("div.listitempage:first").height();
          window.scrollTo(0, $(window).scrollTop()+item_height); // adjust scroll
          prev_data_url = data.prev_data_url;
          prev_data_cache = false;
          $.getJSON(prev_data_url, function(preview_data) {
            prev_data_cache = preview_data;
          });
          if (hide_on_load) {
            $(hide_on_load).hide();
            hide_on_load = false;
          }
        }
        if (prev_data_cache) {
          showPrevious(prev_data_cache);
          is_loading = 0;
        } else {
          $.getJSON(prev_data_url, function(data) {
            showPrevious(data);
            is_loading = 0;
          });
        }
      }
    };

    function mostlyVisible(element) {
      // if ca 25% of element is visible
      var scroll_pos = $(window).scrollTop();
      var window_height = $(window).height();
      var el_top = $(element).offset().top;
      var el_height = $(element).height();
      var el_bottom = el_top + el_height;
      return ((el_bottom - el_height*0.25 > scroll_pos) && 
              (el_top < (scroll_pos+0.5*window_height)));
    }

    function initPaginator() {
      $(window).scroll(function() {
        // handle scroll events to update content
        var scroll_pos = $(window).scrollTop();
        if (scroll_pos >= 0.9*($(document).height() - $(window).height())) {
          if (is_loading==0) loadFollowing();
        }
        if (scroll_pos <= 0.9*$("#header").height()) {
          if (is_loading==0) loadPrevious();
        }
        // Adjust the URL based on the top item shown
        // for reasonable amounts of items
        if (Math.abs(scroll_pos - last_scroll)>$(window).height()*0.1) {
          last_scroll = scroll_pos;
          $(".listitempage").each(function(index) {
            if (mostlyVisible(this)) {
              history.replaceState(null, null, $(this).attr("data-url"));
              $("#pagination").html($(this).attr("data-pagination"));
              return(false);
            }
          });
        }
      });
      $(document).ready(function () {
        // if we have enough room, load the next batch
        if ($(window).height()>$("#scrollingcontent").height()) {
          if (next_data_url!="") {
            loadFollowing();
          } else {
            var filler = document.createElement("div");
            filler.id = "filler";
            filler.style.height = ($(window).height() - 
                    $("#scrollingcontent").height())+ "px";
            $("#scrollingcontent").after(filler);
            hide_on_load = "filler";
          }
        }
        // scroll down to hide empty room
        head_height = $("#header").height();
        window.scrollTo(0, head_height); 
      });
    }

    function primeCache() {
      $.getJSON(prev_data_url, function(data) { prev_data_cache=data; } ); 
      $.getJSON(next_data_url, function(data) { next_data_cache=data; } ); 
    }

})();