Issue when sending multiple images in a GET Method in Nodejs

Question

I am facing issue with sending image in a GET Method in node.js. As you can see in the below code the file is saved in a folder called images and the path of that file is stored in the Object. I tried searching for the file in the directory and then convert it to base64 to send the images but instead all the files in the directory are being converted to base64 and sent. Hence if you could please help me in resolving this issue.

Please let me know if you require any further information from my end.

Router.js

router.get("/users/data/expand/:nid", async (req, res) => {
  var idselected = req.params.nid;
  var dir = "images";
  try {
    const checkData = await user.findOne({ user_id: idselected });

    let receivedFile = await Promise.all(
      checkData.attachments.flatMap(async element => {
        let files = await readDirectory(dir);
        return await Promise.all(
          files.map(filename => {
            filename = element;
            return readFile(filename)
          })
        );
      })
    );
    const returnUser = new User({
      user_id: checkData.user_id,
      attachments: receivedFile
    });
    let savedUser = await returnUser.save();
    res.status(201).send(savedUser);
  } catch (e) {
    res.status(500).send(e);
  }
});

function readDirectory(dir) {
  return new Promise((res, rej) => {
    fs.readdir(dir, function(err, files) {
      if (err) {
        rej(err);
      } else {
        res(files);
      }
    });
  });
}

function readFile(filename) {
  return new Promise((res, rej) => {
    fs.readFile(filename, "base64", (err, base64Data) => {
      if (err) {
        rej(err);
      }
      res(base64Data);
    });
  });
}