Hides all stories in the Facebook news feed except for sponsored advertisements. This is the antithesis to "remove-facebook-ads.js", as requested by /u/datlean.

select-facebook-ads.js

// ==UserScript==
// @name         Select Facebook Ads
// @version      1.0
// @description  Hides all stories in the Facebook news feed except for sponsored advertisements.
// @author       theftprevention
// @match        https://www.facebook.com/
// @grant        none
// ==/UserScript==

(function() {
    'use strict';

    var interval = 1000;
    var reg_sponsored = /^Sponsored$/i;
    var subtitleSelector = "[data-testid='story-subtitle'] > span:first-child";
    var storySelector = "div[data-testid='fbfeed_story']";
    var whitelist = new WeakSet();

    /**
     * @param {HTMLElement} element
     * @returns {string}
     */
    function getDisplayedInnerText(element) {
        var style = getComputedStyle(element);
        if (style.display === 'none') {
            return '';
        }
        var child;
        var children = element.childNodes;
        var text = '';
        for (var i = 0, l = children.length; i < l; i++) {
            child = children[i];
            switch (child.nodeType) {
                case Node.ELEMENT_NODE:
                    text += getDisplayedInnerText(child);
                    break;
                case Node.TEXT_NODE:
                    text += child.textContent;
                    break;
            }
        }
        return text;
    }

    /**
     * @returns {void}
     */
    function selectAds() {
        var element;
        var elements = document.querySelectorAll(storySelector);
        var i = elements.length;
        var subtitle;

        while (i--) {
            element = elements[i];
            if (whitelist.has(element)) {
                continue;
            }
            whitelist.add(element);
            subtitle = element.querySelector(subtitleSelector);
            if (!subtitle || !reg_sponsored.test(getDisplayedInnerText(subtitle))) {
                element.style.display = 'none';
            }
        }
    }

    /**
     * @returns {void}
     */
    function initialize() {
        document.removeEventListener('DOMContentLoaded', initialize);
        setInterval(selectAds, interval);
    }

    if (document.readyState === 'loading') {
        document.addEventListener('DOMContentLoaded', initialize);
    } else {
        initialize();
    }

})();