jav101.js

if (location.pathname.startsWith('/play')) {
  (() => {

    function downloadVideo(print = console.log) {
      let url =
        document
          .querySelector('video')
          .firstElementChild
          .getAttribute('src');

      let dir = url.slice(0, url.lastIndexOf('/') + 1);

      let finished = 0;
      let total;

      function getList(link) {
        return new Promise(resolve => {
          let xhr = new XMLHttpRequest();
          xhr.withCredentials = true;
          xhr.onreadystatechange = () => {
            if (xhr.readyState == 4) {
              resolve(
                xhr
                  .responseText
                  .trim()
                  .split('\n')
                  .filter(url => url[0] !== '#')
              );
            }
          };
          xhr.open('GET', link, true);
          xhr.send();
        });
      }

      function getBlob(link) {
        return new Promise(resolve => {
          let xhr = new XMLHttpRequest();
          xhr.responseType = 'blob';
          xhr.withCredentials = true;
          xhr.onreadystatechange = () => {
            if (xhr.readyState == 4) {
              print(`${Math.round(10000 * ++finished / total) / 100}%`);
              resolve(xhr.response);
            }
          };
          xhr.open('GET', link, true);
          xhr.send();
        });
      }

      return new Promise(resolve => {
        getList(url)
          .then(list => {
            total = list.length;

            Promise
              .all(list.map(file => getBlob(dir + file)))
              .then(blobs => {
                let blob = new Blob(blobs, { type: 'text/vnd.trolltech.linguist' });

                let a = document.createElement('a');
                a.href = URL.createObjectURL(blob);
                a.download = `${document.title}.mpeg`;

                a.click();
                resolve();
              });
          });
      });
    }

    function addDownloadButton() {
      let button = document.createElement('div');
      button.classList.add('video-action-btn', 'download');

      let icon = document.createElement('i');
      icon.classList.add('glyphicon', 'glyphicon-save', 'downloadIcon');
      button.appendChild(icon);

      let text = document.createElement('span');
      text.classList.add('text');
      text.innerText = '幹你娘載爆';
      button.appendChild(text);

      document.querySelector('.video-action').appendChild(button);

      let downloading = false;

      button.onclick = () => {
        if (downloading) {
          alert('已在下載中');
          return;
        }

        downloading = true;

        downloadVideo((message) => {
          text.innerText = message;
        }).then(() => {
          text.innerText = '幹你娘載爆';
          downloading = false;
        });
      };
    }

    // downloadVideo();
    addDownloadButton();

  })();
}