index.html

<input type="file" id="file" multiple="true" />
<input type="button" onclick="run()" value="Upload" />
<div id="progress"></div>

<script src="https://cdn.jsdelivr.net/gh/tanaikech/ResumableUploadForGoogleDrive_js@master/resumableupload_js.min.js"></script>
<script>
  function run() {
    google.script.run
      .withSuccessHandler(accessToken =>
        ResumableUploadForGoogleDrive(accessToken)
      )
      .getAuth();
  }

  function ResumableUploadForGoogleDrive(accessToken) {
    const f = document.getElementById("file");
    [...f.files].forEach((file, i) => {
      let fr = new FileReader();
      fr.fileName = file.name;
      fr.fileSize = file.size;
      fr.fileType = file.type;
      fr.readAsArrayBuffer(file);
      fr.onload = e => {
        var id = "p" + ++i;
        var div = document.createElement("div");
        div.id = id;
        document.getElementById("progress").appendChild(div);
        document.getElementById(id).innerHTML = "Initializing.";
        const f = e.target;
        const resource = {
          fileName: f.fileName,
          fileSize: f.fileSize,
          fileType: f.fileType,
          fileBuffer: f.result,
          accessToken: accessToken
        };
        const ru = new ResumableUploadToGoogleDrive();
        ru.Do(resource, function(res, err) {
          if (err) {
            console.log(err);
            return;
          }
          console.log(res);
          let msg = "";
          if (res.status == "Uploading") {
            msg =
              Math.round(
                (res.progressNumber.current / res.progressNumber.end) * 100
              ) +
              "% (" +
              f.fileName +
              ")";
          } else {
            msg = res.status + " (" + f.fileName + ")";
          }

          // If you want to put the uploaded file information to the active Spreadsheet,
          // please use the following function.
          if (res.status == "Done") google.script.run.putFileInf(res.result);

          document.getElementById(id).innerText = msg;
        });
      };
    });
  }
</script>