Reddit Old Infinite Scroll

Infinite scroll (autopagerize) for old.reddit.com. Prefetches early and ads a visible page note.
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// ==UserScript==
// @name         Reddit Old Infinite Scroll
// @namespace    https://github.com/BD9Max
// @version      1.0
// @description  Infinite scroll (autopagerize) for old.reddit.com. Prefetches early and ads a visible page note.
// @author       krbd9max
// @match        https://old.reddit.com/*
// @exclude      https://old.reddit.com/prefs*
// @exclude      https://old.reddit.com/message*
// @grant        none
// @run-at       document-idle
// @license      MIT
// ==/UserScript==

(function() {
    'use strict';

    let isLoading = false;
    let nextPageUrl = null;
    let pageCount = 1;

    // --- CONFIGURATION ---
    const TRIGGER_THRESHOLD = 1700; // pixel distance from bottom until prefetch
    const SEPARATOR_TEXT = "--- PAGE {n} ---";

    // CSS page divider
    const style = document.createElement('style');
    style.textContent = `
        .pager-separator {
            clear: both;
            display: flex;
            align-items: center;
            justify-content: center;
            margin: 40px 0;
            padding: 10px;
            font-family: verdana, arial, helvetica, sans-serif;
        }
        .pager-separator::before, .pager-separator::after {
            content: "";
            flex: 1;
            height: 1px;
            background: #cee3f8;
            margin: 0 20px;
        }
        .pager-note {
            color: #888;
            font-size: 10px;
            font-weight: bold;
            letter-spacing: 2px;
            text-transform: uppercase;
        }
        .nav-buttons { display: none !important; } /* Hides original next/prev buttons */
    `;
    document.head.appendChild(style);

    function getNextUrl() {
        const nextButton = document.querySelector('.next-button a');
        return nextButton ? nextButton.href : null;
    }

    function createSeparator(num) {
        const div = document.createElement('div');
        div.className = 'pager-separator';
        div.innerHTML = `<span class="pager-note">${SEPARATOR_TEXT.replace('{n}', num)}</span>`;
        return div;
    }

    async function loadNextPage() {
        if (isLoading) return;
        
        const url = nextPageUrl || getNextUrl();
        if (!url) return;

        isLoading = true;
        console.log("Loading next page:", url);

        try {
            const response = await fetch(url);
            const html = await response.text();
            const parser = new DOMParser();
            const doc = parser.parseFromString(html, 'text/html');

            const siteTable = document.querySelector('#siteTable');
            const newPosts = doc.querySelectorAll('#siteTable > .thing');
            const nextBtn = doc.querySelector('.next-button a');

            if (newPosts.length > 0) {
                pageCount++;
                siteTable.appendChild(createSeparator(pageCount));

                newPosts.forEach(post => {
                    // Update rank numbers to continue the sequence
                    const rank = post.querySelector('.rank');
                    if (rank && rank.innerText) {
                        const currentMax = document.querySelectorAll('#siteTable > .thing').length;
                        rank.innerText = parseInt(rank.innerText) || '';
                    }
                    siteTable.appendChild(post);
                });

                // Update the URL for the next fetch
                nextPageUrl = nextBtn ? nextBtn.href : null;
                
                // Trigger any Reddit-native JS for the new elements (like expando buttons)
                if (window.reddit && window.reddit.setup_expandos) {
                    window.reddit.setup_expandos();
                }
            } else {
                nextPageUrl = null; // No more pages
            }
        } catch (err) {
            console.error("Error loading next page:", err);
        } finally {
            isLoading = false;
        }
    }

    // Scroll listener with throttle-like check
    window.addEventListener('scroll', () => {
        const scrollPos = window.innerHeight + window.pageYOffset;
        const pageHeight = document.documentElement.scrollHeight;

        // If we are within TRIGGER_THRESHOLD of the bottom, load the next page
        if (scrollPos >= pageHeight - TRIGGER_THRESHOLD) {
            loadNextPage();
        }
    });

    // Initial check in case the page is very short
    if (document.documentElement.scrollHeight <= window.innerHeight + TRIGGER_THRESHOLD) {
        loadNextPage();
    }
})();