Can't figure out how to select items in the Facebook newsfeed for a Chome Extension - facebook

Question

I'm working on a Chrome extension that inserts a button on every item in the Facebook newsfeed. I started off by using Tampermonkey to install a script that installs a button next to the subscribe video of every Youtube page (chrome-extension://dhdgffkkebhmkfjojejmpbldmpobfkfo/ask.html?aid=994ff494-1242-452f-a334-1bd616e18bb6), which worked fine.
Then I tried to modify it so it acts on the Facebook newsfeed, rather than the Youtube subscribe button. I changed the // match to go to facebook.com and targeting it to go after class='_3vuz', the Facebook div that houses the "like" button. But nothing happens when I go on Facebook; no button appears.
Here's my Tampermonkey code. Many thanks!
// ==UserScript==
// #name Facebook Fake News Button
// #namespace https://www.youtubeinmp3.com
// #version 1.2.2
// #description Adds a button to show you whether a Facebook article is true
// #author Ilana
// #match https://www.facebook.com/*
// #run-at document-end
// ==/UserScript==
function polymerInject(){
/* Create button */
var buttonDiv = document.createElement("div");
buttonDiv.style.width = "100%";
buttonDiv.id = "parentButton";
var addButton = document.createElement("button");
addButton.appendChild(document.createTextNode("Fake News"));
if(typeof(document.getElementById("iframeDownloadButton")) != 'undefined' && document.getElementById("iframeDownloadButton") !== null){
document.getElementById("iframeDownloadButton").remove();
}
addButton.style.width = "100%";
addButton.style.backgroundColor = "#181717";
addButton.style.color = "white";
addButton.style.textAlign = "center";
addButton.style.padding = "10px 0";
addButton.style.marginTop = "5px";
addButton.style.fontSize = "14px";
addButton.style.border = "0";
addButton.style.cursor = "pointer";
addButton.style.borderRadius = "2px";
addButton.style.fontFamily = "Roboto, Arial, sans-serif";
addButton.onclick = function () {
this.remove();
/* Add large button on click */
var addIframe = document.createElement("iframe");
addIframe.src = '//www.convertmp3.io/widget/button/?color=ba1717&video=' + window.location.href;
addIframe.style.width = "100%";
addIframe.style.border = "none";
addIframe.style.height = "60px";
addIframe.style.marginTop = "10px";
addIframe.style.overflow = "hidden";
addIframe.scrolling = "no";
addIframe.id = "iframeDownloadButton";
var targetElement = document.querySelectorAll("[id='meta']");
for(var i = 0; i < targetElement.length; i++){
if(targetElement[i].className.indexOf("ytd-watch") > -1){
targetElement[i].insertBefore(addIframe, targetElement[i].childNodes[0]);
}
}
};
buttonDiv.appendChild(addButton);
/* Find and add to target */
var targetElement = document.querySelectorAll("[class='_3vuz']");
for(var i = 0; i < targetElement.length; i++){
if(targetElement[i].className.indexOf("ytd-video-secondary-info-renderer") > -1){
targetElement[i].appendChild(buttonDiv);
}
}
/* Fix hidden description bug */
var descriptionBox = document.querySelectorAll("ytd-video-secondary-info-renderer");
if(descriptionBox[0].className.indexOf("loading") > -1){
descriptionBox[0].classList.remove("loading");
}
}
function standardInject() {
var pagecontainer=document.getElementById('page-container');
if (!pagecontainer) return;
if (/^https?:\/\/www\.facebook.com\/watch\?/.test(window.location.href)) run();
var isAjax=/class[\w\s"'-=]+spf\-link/.test(pagecontainer.innerHTML);
var logocontainer=document.getElementById('logo-container');
if (logocontainer && !isAjax) { // fix for blocked videos
isAjax=(' '+logocontainer.className+' ').indexOf(' spf-link ')>=0;
}
var content=document.getElementById('content');
if (isAjax && content) { // Ajax UI
var mo=window.MutationObserver||window.WebKitMutationObserver;
if(typeof mo!=='undefined') {
var observer=new mo(function(mutations) {
mutations.forEach(function(mutation) {
if(mutation.addedNodes!==null) {
for (var i=0; i<mutation.addedNodes.length; i++) {
if (mutation.addedNodes[i].id=='watch7-container' ||
mutation.addedNodes[i].id=='watch7-main-container') { // old value: movie_player
run();
break;
}
}
}
});
});
observer.observe(content, {childList: true, subtree: true}); // old value: pagecontainer
} else { // MutationObserver fallback for old browsers
pagecontainer.addEventListener('DOMNodeInserted', onNodeInserted, false);
}
}
}
function onNodeInserted(e) {
if (e && e.target && (e.target.id=='watch7-container' ||
e.target.id=='watch7-main-container')) { // old value: movie_player
run();
}
}
function finalButton(){
var buttonIframeDownload = document.createElement("iframe");
buttonIframeDownload.src = '//www.convertmp3.io/widget/button/?color=ba1717&video=' + window.location.href;
buttonIframeDownload.id = "buttonIframe";
buttonIframeDownload.style.width = "100%";
buttonIframeDownload.style.height = "60px";
buttonIframeDownload.style.paddingTop = "20px";
buttonIframeDownload.style.paddingBottom = "20px";
buttonIframeDownload.style.overflow = "hidden";
buttonIframeDownload.scrolling = "no";
document.getElementById("watch-header").appendChild(buttonIframeDownload);
}
function run(){
if(!document.getElementById("parentButton") && window.location.href.substring(0, 25).indexOf("facebook.com") > -1 && window.location.href.indexOf("watch?") > -1){
var parentButton = document.createElement("div");
parentButton.className = "yt-uix-button yt-uix-button-default";
parentButton.id = "parentButton";
parentButton.style.height = "23px";
parentButton.style.marginLeft = "28px";
parentButton.style.paddingBottom = "1px";
parentButton.onclick = function () {
this.remove();
finalButton();
};
document.getElementById("watch7-user-header").appendChild(parentButton);
var childButton = document.createElement("span");
childButton.appendChild(document.createTextNode("Download MP3"));
childButton.className = "yt-uix-button-content";
childButton.style.lineHeight = "25px";
childButton.style.fontSize = "12px";
parentButton.appendChild(childButton);
}
}
if(document.getElementById("polymer-app") || document.getElementById("masthead") || window.Polymer){
setInterval(function(){
if(window.location.href.indexOf("watch?v=") < 0){
return false;
}
if(document.getElementById("count") && document.getElementById("parentButton") === null){
polymerInject();
}
}, 100);
}
else{
standardInject();
}