scripts/userscripts/messenger-dynamic-sidebar.user.js

// ==UserScript==
// @name        Dynamic Sidebar
// @namespace   tretrauit-dev
// @match       *://www.messenger.com
// @icon        https://genshin.hoyoverse.com/favicon.ico
// @grant       none
// @version     1.0
// @author      tretrauit
// @description Dynamic Sidebar for Facebook Messenger (messenger.com)
// @homepageURL https://gitlab.com/tretrauit/scripts
// @supportURL  https://gitlab.com/tretrauit/scripts/-/issues
// @downloadURL https://git.tretrauit.me/tretrauit/scripts/raw/branch/main/userscripts/messenger-dynamic-sidebar.user.js
// ==/UserScript==

function injectCSS(css) {
	const style = document.createElement("style");
	style.appendChild(document.createTextNode(css));
	document.head.appendChild(style);
}

function findElement(tag, properties) {
	const elements = document.querySelectorAll(tag);
	elementLoop: for (const element of elements) {
		for (const [key, value] of Object.entries(properties)) {
			if (element.getAttribute(key) !== value) {
				continue elementLoop;
			}
		}
		return element;
	}
}

function getAncestor(element, level) {
	if (element == null) {
		return null;
	}
	for (let i = 0; i < level; i++) {
		element = element.parentNode;
	}
	return element;
}

console.log("Scanning class for components...");
// Search box
let searchBox = findElement("input", { "aria-autocomplete": "list" });
if (searchBox == null) {
	console.warn("Failed to get searchBox element.");
	throw new Error();
}
searchBox = getAncestor(searchBox, 7);
// Header & Text header
let textHeader = findElement("span", {
	style:
		"line-height: var(--base-line-clamp-line-height); --base-line-clamp-line-height:28px;",
});
let header;
if (textHeader == null) {
	console.warn("Failed to get textHeader element.");
	throw new Error();
}
header = getAncestor(textHeader, 7);
textHeader = textHeader.childNodes[0];
// Unread indicator
let unreadIndicator = findElement("span", {
	"data-visualcompletion": "ignore",
});
// Action bar
let actionBar = findElement("div", { "aria-expanded": "false" });
if (actionBar == null) {
	console.warn("Failed to get actionBar element.");
	throw new Error();
}
actionBar = actionBar.parentNode;
// Chats
let chats = findElement("div", { "aria-label": "Chats" });
if (chats == null) {
	console.warn("Failed to get chats element.");
	throw new Error();
}
chats = chats.parentNode;
// Print elements
console.log("Search box:", searchBox);
console.log("Header:", header);
console.log("Text header:", textHeader);
console.log("Unread message indicator:", unreadIndicator);
console.log("Action bar:", actionBar);
console.log("Chat tab:", chats);