Build an API Proxy with Node.js and Express

const express = require('express');
const fetch = require('node-fetch'); // For Node.js, install with `npm install node-fetch@2` for CommonJS or use native fetch in newer Node.js
const cors = require('cors'); // Install with `npm install cors`
const dotenv = require('dotenv'); // Install with `npm install dotenv`

dotenv.config(); // Load environment variables from .env file

const app = express();
const PORT = process.env.PORT || 3000;
const TARGET_API_URL = 'https://jsonplaceholder.typicode.com/posts'; // Example public API
const API_KEY = process.env.THIRD_PARTY_API_KEY; // Store sensitive keys in .env

// Enable CORS for all origins, or configure specific origins for production
app.use(cors());

// Middleware to log requests (optional)
app.use((req, res, next) => {
  console.log(`Proxying request: ${req.method} ${req.originalUrl}`);
  next();
});

// Proxy endpoint
app.get('/api/proxy', async (req, res) => {
  try {
    // Construct the target URL. You might append query parameters from req.query
    const fullTargetUrl = `${TARGET_API_URL}${req.query.id ? '/' + req.query.id : ''}`;

    // Example of adding an API key to the request to the third-party API
    const headers = {
      'Content-Type': 'application/json',
      // 'Authorization': `Bearer ${API_KEY}` // Uncomment if your API uses Bearer token auth
      // 'x-api-key': API_KEY // Uncomment if your API uses a custom header for API key
    };

    const response = await fetch(fullTargetUrl, { headers: headers });

    if (!response.ok) {
      return res.status(response.status).json({ error: 'Failed to fetch from external API' });
    }

    const data = await response.json();
    res.json(data); // Send the data received from the external API back to the client
  } catch (error) {
    console.error('Proxy error:', error);
    res.status(500).json({ error: 'Internal server error during proxy request' });
  }
});

app.listen(PORT, () => {
  console.log(`Proxy server listening on port ${PORT}`);
  console.log(`Try: http://localhost:${PORT}/api/proxy`);
  console.log(`Try: http://localhost:${PORT}/api/proxy?id=1`);
});