mastothing.user.js

// ==UserScript==
// @name Mastodon timeline thing
// @description keep timeline from automatically scrolling under mouse cursor
// @author @revenant@mastodon.social
// @version 0.1
// @include https://mastodon.social/*
// @run-at document-idle
// @namespace revenant.mastodon
// ==/UserScript==

(function () {
	"use strict";

	// watch for added/removed child nodes for selected nodes and all child nodes
	var observerInit = { childList: true, subtree: true };

	// callback for when a status (or something else) is added to a timeline
	var columnModified = function(recs) {
		recs.forEach(function (rec) {
			// keep the timeline scrolled down to the same spot
			var scrollable = rec.target.closest(".scrollable");
			if (scrollable !== null && scrollable.scrollTop === 0) {
				rec.addedNodes.forEach(function(node) {
					scrollable.scrollTop += node.scrollHeight;
				});
			}
		});
	};

	// watch for timelines being shown/hidden
	new MutationObserver(function(recs) {
		recs.forEach(function (rec) {
			rec.addedNodes.forEach(function (node) {
				if (node.className == "column") {
					var itemlist = node.getElementsByClassName("item-list")[0];
					if (itemlist == null) return;

					itemlist._statusObserver = new MutationObserver(columnModified);

					// monitor a timeline if the user puts the mouse over it
					itemlist.addEventListener("mouseenter", function() {
						itemlist._statusObserver.observe(itemlist, { childList: true });
					});

					// stop monitoring that timeline when the cursor leaves
					itemlist.addEventListener("mouseleave", function() {
						itemlist._statusObserver.disconnect();
					});
				}
			});

			rec.removedNodes.forEach(function (node) {
				if (node.className == "column") {
					var itemlist = node.getElementsByClassName("item-list")[0];
					if (itemlist == null) return;

					delete itemlist._statusObserver;
				}
			});
		});
	}).observe(document.getElementsByClassName("columns-area")[0], observerInit);

})();