twitter-yomiage.js

const speak = (body) => {
  const synth = window.speechSynthesis;
  const allVoices = synth.getVoices();
  const jaVoices = allVoices.filter(v=> v.lang === 'ja-JP');
  const voice = jaVoices[0];
  if (!voice) { 
    throw new Error('voice not found');
  }

  const utter = new SpeechSynthesisUtterance(body);
  utter.voice=voice;
  utter.lang = 'ja-JP';
  utter.pitch = 1
  utter.volume = 1
  utter.rate = 1

  synth.speak(utter)
}

const listen = () => {
  new MutationObserver((mutations, observer) => {
    for (const m of mutations) {
      if (m.type!=='childList') {
        continue
      }
      const body = m.target.querySelector('div[lang]>span')
      if (!body) {
        continue
      }
      speak(body.textContent)
    }
  }).observe(document.querySelector('[aria-label="タイムライン: ホームタイムライン"'), {
    childList: true,
    subtree: true,
  })
}
listen()