UserScript for forcing links to open in the same tab

noNewTabs.js

// ==UserScript==
// @name         Force links to open in same window
// @namespace    https://github.com/scarlac
// @version      1.1.0
// @description  Rewrite target="_blank" (and similar) on links, areas, forms, and base tags so navigation stays in the current window/tab. Does not touch window.open or other JS APIs.
// @author       scarlac
// @match        *://*/*
// @run-at       document-start
// @grant        none
// @noframes
// ==/UserScript==

/**
 * This script was written to address the user-hostile practice
 * where many websites decide that you MUST open a new tab, as if you had no capacity to manage it yourself.
 * The modern equivalent of pop-ups from the 90'ies.
 * And since Chrome does not seem to have a native feature to disable this, you end up with a million mental threads.
 * The Observer is necessary for sites like React. It does not fix all links as some sites use window.open and other dynamic tricks.
 *
 * Tested with TamperMonkey for Chrome.
 **/

(function () {
	'use strict';

	const BAD_TARGETS = new Set(['_blank', '_new', 'blank', 'new']);
	const SELECTOR = 'a[target], area[target], form[target], base[target]';

	function fixTarget(el) {
		if (!el || !el.getAttribute) return;
		const t = el.getAttribute('target');
		if (t && BAD_TARGETS.has(t.toLowerCase())) {
			el.setAttribute('target', '_self');
		}
	}

	function scan(root) {
		if (!root || !root.querySelectorAll) return;
		root.querySelectorAll(SELECTOR).forEach(fixTarget);
	}

	// Initial sweep as soon as the DOM is parseable.
	if (document.readyState === 'loading') {
		document.addEventListener('DOMContentLoaded', () => scan(document), { once: true });
	} else {
		scan(document);
	}

	// Watch for dynamically added/changed elements (SPAs, infinite scroll, etc.).
	const mo = new MutationObserver((mutations) => {
		for (const m of mutations) {
			if (m.type === 'attributes') {
				fixTarget(m.target);
			} else {
				m.addedNodes.forEach((node) => {
					if (node.nodeType !== 1) return; // Element nodes only
					fixTarget(node);
					scan(node);
				});
			}
		}
	});

	const startObserver = () => {
		mo.observe(document.documentElement || document, {
			subtree: true,
			childList: true,
			attributes: true,
			attributeFilter: ['target'],
		});
	};

	if (document.documentElement) {
		startObserver();
	} else {
		document.addEventListener('readystatechange', startObserver, { once: true });
	}
})();