Youtubeに音量調節用スライダー設置

var result = document.evaluate('//video', document, null, 7, null);
document.getElementById("info-text").insertAdjacentHTML('afterend', '<input type="range" name="example" step="5" max="100" id="hoge">');
document.getElementById("hoge").addEventListener('change', function () {
  result.snapshotItem(0).volume = document.getElementById("hoge").value/100;
  this.title = document.getElementById("hoge").value + "%";
}, false);