Node.js CORS error persists even when cors() middleware is enabled

❓ Problem Statement I enabled CORS using Express’s cors() middleware in my Node.js API, but browser errors still say: “No 'Access-Control-Allow-Origin' header is present…”

This is often caused by: • Incorrect middleware ordering or parameters • Failing to explicitly handle OPTIONS preflight • Omitting required headers (like custom or X-Requested-With) • Or mistakenly importing from a file named cors.json, not the cors packageStack Overflow+4Stack Overflow+4Stack Overflow+4Stack OverflowStack OverflowStack Overflow

🛠️ Fixes:

1. Correct Middleware Setup Place the middleware before routes and ensure you don’t shadow import: js CopyEdit const cors = require('cors'); app.use(cors({ origin: 'http://localhost:3000', credentials: true })); app.options('*', cors()); // needed for preflight If you're using routers, ensure the cors() setup is applied globally or within those routers tooStack Overflow.
2. Properly Handle OPTIONS Requests Some requests (like custom headers or non-simple methods) require preflight handling: js CopyEdit app.options('*', cors(corsOptions)); or register it per route. Always respond with correct headersStack Overflow.
3. Include All Necessary Headers If the client sends headers like X-Requested-With, include them in allowedHeaders. For example: js CopyEdit const corsOptions = { origin: 'http://localhost:3000', methods: ['GET', 'POST', 'PUT', 'DELETE'], allowedHeaders: ['Authorization','Content-Type','X-Requested-With'], credentials: true }; Missing configuration here can lead to failures even if other headers appear correctStack Overflow+2Stack Overflow+2Stack Overflow+2.
4. Don’t Overwrite Middleware Import Ensure you're not loading a file named cors.json by mistake. The error may come from the wrong import—check your filenamesStack Overflow.

🧩 TL;DR Even with cors() installed, CORS errors persist if middleware is misplaced, preflight requests aren’t handled, necessary headers aren’t allowed, or there's an import naming collision.

🧷 Suggested Tags: nodejs, express, cors, cross-origin, preflight, javascript, http