blob-to-buffer.js

  async convertBlobToBuffer(blob) {
    let fileReader = new FileReader();

    // Listen to when reading is finished and 
    // run the callback with a buffer.
    let loadEnd = new Promise((resolve, reject) => {
      fileReader.addEventListener("loadend", (ev) => {
        if (ev.error) {
          reject(ev.error);
        }
        else {
          resolve(new Buffer(fileReader.result));
        }
      }, false);
    });

    // Read the blob as a typed array.
    fileReader.readAsArrayBuffer(blob);
    return await loadEnd;
  }