Audio won't be muted with JavaScript - removing audio tags with mutationobserver needed

Question

I tried to use the following userscript to remove all audio from a certain website:

// ==UserScript==
// @name        addicto
// @namespace   nms
// @include     http://*
// @include     https://*
// @version     1
// @grant       none
// ==/UserScript==

addEventListener('DOMContentLoaded', ()=>{
  let sites = ['mako.co.il'];
  let href = window.location.href;
  for (let i = 0; i < sites.length; i++) {
    if (href.includes(sites[i])) {
      Array.prototype.slice.call(document.querySelectorAll('audio')).forEach((audio)=>{
        audio.muted = true;
      });
    }
  }

  // If href includes the value of the iteration on the "sites" array, do stuff.
});

This code didn't work and I assume that observing all audio tags coming randomly and mutating the DOM is exactly what I need to better cope with this.

How can this mutation observer be written? I have never written a mutation observer and I feel as if this example would be very short and very basic and exactly what I need to get a taste of the code context of the logic which I just described and I would thank dearly to anyone who will try to show it to me and other people who are having a similar problem.

Answer 1

• Enumerate mutations and each mutation's addedNodes
• Enumerate node's child elements because mutations are coalesced during page loading using the superfast getElementsByTagName instead of the superslow querySelectorAll
• Don't use @grant none, which runs your userscript in the page context, unless you really need direct access to the page's JavaScript objects
• Use @run-at document-start to mute the audio during page loading

// ==UserScript==
// @name     addicto
// @include  *
// @run-at   document-start
// ==/UserScript==

const sites = ['mako.co.il'];
if (sites.some(site => location.hostname.includes(site))) {
  new MutationObserver(mutations => {
    for (const m of mutations) {
      for (const node of m.addedNodes) {
        if (node.localName == 'audio') {
          audio.muted = true;
        } else if (node.firstElementChild) {
          for (const child of node.getElementsByTagName('audio')) {
            audio.muted = true;
          }
        }
      }
    }
  }).observe(document, {subtree: true, childList: true});
}