Memorizing tweet scroll position

tw_tspm.js

// ==UserScript==
// @name         Twitter Tweet Scroll Position Memorizer
// @namespace    https://estar-lab.net/
// @version      1.0
// @description  Memorizing tweet scroll position
// @author       silver-mixer
// @match        https://twitter.com/*
// @icon         https://www.google.com/s2/favicons?sz=64&domain=twitter.com
// @grant        none
// ==/UserScript==

(() => {
	'use strict';
	const MAX_SCROLL_HISTORIES = 10;
	let scrollPositionMap = new Map();
	let lastUrl = null;
	window.addEventListener('scroll', () => {
		let url = location.href;
		if(url.includes('/status/')){
			if(scrollPositionMap.has(url)){
				if(lastUrl !== url){
					window.scrollBy(window.scrollX, scrollPositionMap.get(url));
				}
				scrollPositionMap.delete(url);
			}
			scrollPositionMap.set(url, window.scrollY);
			if(scrollPositionMap.size > MAX_SCROLL_HISTORIES){
				scrollPositionMap.delete(scrollPositionMap.keys().next().value);
			}
			lastUrl = url;
		}
	});
})();