Native handling of file upload in NodeJs - no library

client.js

const inputButton = document.getElementById("inputtag");
const buttonn = document.querySelector(".btn");
inputButton.addEventListener("change", async (e) => await updateFile(e));
buttonn.addEventListener("click", () => uploadFile());

let data = null;
async function updateFile(e) {
  const file = e.target.files[0];

  const formData = new FormData();
  formData.append("image", file);
  data= formData;
}
async function uploadFile() {
  try {
    const imageData = await fetch("http://localhost:5000/upload", {
      method: "POST",
      headers: {
        "Content-Type": "multipart/form-data",
      },
      body: data,
    });
  } catch (err) {
    console.log(err);
  }
}

endpoint.js

app.post("/upload", async (req, res) => {
  
let data = [];
  req.on("data", (chunk) => {
    data.push(chunk);
  });

  req.on("end", () => {
    let fileData = Buffer.concat(data);
    fs.writeFile(
      path.join(__dirname, "example.pdf"),
      fileData,
      "base64",
      (err) => {
        if (err) {
          res.statusCode = 500;
        }
      }
    );
  });
});