Express JS file upload

uploader.js

const express = require("express");
const multer = require("multer");
const fs = require("fs");
const path = require("path");
const port = process.env.PORT || 3000;
const app = express();

const upload = multer({
  dest: "./uploads",
});

app.post("/upload", upload.single("file"), (req, res) => {
  const tempPath = req.file.path;
  const targetPath = path.join(__dirname, `./uploads/${req.file.originalname}`);

  if (path.extname(req.file.originalname).toLowerCase() === ".png") {
    fs.rename(tempPath, targetPath, (err) => {
      if (err) {
        return res.status(500).json({ error: err });
      }

      res.status(200).contentType("text/plain").end("File uploaded!");
    });
  } else {
    fs.unlink(tempPath, (err) => {
      if (err) {
        return res.status(500).json({ error: err });
      }

      res
        .status(403)
        .contentType("text/plain")
        .end("Only .png files are allowed!");
    });
  }
});

app.listen(port, () => console.log("WORKING"));