node js validate body without middleware

const express = require('express');
const app = express();

app.use(express.json());

app.post('/validate', (req, res) => {
  const { body } = req;

  if (!body || typeof body !== 'object') {
    return res.status(400).json({ error: 'Invalid request body' });
  }

  const requiredFields = ['field1', 'field2', 'field3'];

  for (const field of requiredFields) {
    if (!(field in body)) {
      return res.status(400).json({ error: `${field} is required` });
    }
  }

  // Additional validation logic for individual fields if needed

  res.json({ success: true });
});

const PORT = process.env.PORT || 3000;
app.listen(PORT, () => {
  console.log(`Server is running on port ${PORT}`);
});