TamperMonkey: force noopener for window-spawning links (Google Chrome)

tampermonkey.noopener.js

// ==UserScript==
// @name         force noopener for window-spawning links
// @namespace    *
// @version      0.1
// @description  adds rel="noopener" to <a href="…" target="_blank">
// @author       Rodney Rehm
// @match        http://*/*
// @grant        none
// ==/UserScript==

// see https://jakearchibald.com/2016/performance-benefits-of-rel-noopener/

(function() {
    'use strict';

    const safeTargets = new Set(['_self', '_parent', '_top']);

    function patchLink(element) {
        const rel = element.getAttribute('rel') || '';
        if (rel.indexOf('noopener') === -1) {
            element.setAttribute('rel', rel + ' noopener');
            console.log("patching", element);
        }
    }

    function patchLinks(context) {
        // find all links that open in a new window by way of the target attribute
        const links = context.querySelectorAll('a[target]');
        const windowSpawningLinks = Array.from(links).filter(element => !safeTargets.has(element.target.trim()));
        // add rel="noopener" to the links opening new windows/tabs
        windowSpawningLinks.forEach(patchLink);
    }

    // patch current DOM
    patchLinks(document);

    // make sure future mutations are considered as well
    const observer = new MutationObserver(function(mutations) {
        mutations.forEach(function(mutation) {
            console.info('MUTATION MUTATION');
            if (mutation.type === 'attributes') {
                patchLink(mutation.target);
            } else if (mutation.type === 'childList') {
                patchLinks(mutation.target);
            }
        });
    });

    observer.observe(document.body, {
        subtree: true,
        attributes: true,
        attributeFilter: ['target'],
    });
})();