Express server scenarios to handle CORS preflight requests properly with custom middleware
I've spent hours debugging this and I'm optimizing some code but I'm a bit lost with This might be a silly question, but I'm working on a personal project and I'm currently building a REST API using Express 4.17 and I've run into a question with CORS handling, specifically with preflight requests... I have a custom middleware to set CORS headers, but it seems that the preflight requests (OPTIONS) are not being handled correctly, resulting in a 404 behavior. My custom middleware is set up like this: ```javascript const express = require('express'); const app = express(); app.use((req, res, next) => { res.header('Access-Control-Allow-Origin', '*'); res.header('Access-Control-Allow-Headers', 'Origin, X-Requested-With, Content-Type, Accept'); if (req.method === 'OPTIONS') { res.sendStatus(200); } else { next(); } }); app.get('/api/data', (req, res) => { res.json({ message: 'Success' }); }); const PORT = process.env.PORT || 3000; app.listen(PORT, () => { console.log(`Server running on port ${PORT}`); }); ``` When I make a CORS request from the frontend, I'm seeing the following in the console: ``` Access to fetch at 'http://localhost:3000/api/data' from origin 'http://localhost:3001' has been blocked by CORS policy: The 'Access-Control-Allow-Origin' header has a value 'null' that is not allowed according to the CORS policy. ``` In the browser's Network tab, I can see that the preflight request is being sent, but it returns a 404 instead of the expected 200 status. I've tried moving the middleware around and even using the `cors` package, but it didn't seem to resolve the scenario. Here's what I've tried: - Install and use the `cors` middleware, but it resulted in the same 404 behavior for OPTIONS requests. - Added a logging statement in my middleware to confirm that the request is hitting it, which it is. - Explicitly defined the `OPTIONS` route: ```javascript app.options('/api/data', (req, res) => { res.sendStatus(200); }); ``` Despite these attempts, the preflight requests are still not being handled correctly. How can I properly configure my Express server to handle CORS preflight requests without running into this scenario? For context: I'm using Javascript on Windows. How would you solve this? What's the best practice here? I'd be grateful for any help. I'm working in a Windows 11 environment. What am I doing wrong?