How to Fix CORS Blocked Error in TypeScript

If you've encountered a CORS Blocked Error while working with TypeScript, you're not alone. This is one of the most common issues developers face.

What Causes This Error

This error occurs when a browser blocks a cross-origin request because the server doesn't include the proper Access-Control-Allow-Origin headers. It's a security mechanism that prevents unauthorized domains from accessing your API.

The Fix

The key is to configure CORS with explicit origins and allowed methods:

import cors from "cors";

const corsOptions = {
  origin: ["https://yourdomain.com"],
  methods: ["GET", "POST", "PUT", "DELETE"],
  credentials: true,
};

app.use(cors(corsOptions));

Common Pitfall

A common mistake is to ignore this error during development because it only surfaces under specific conditions. Always test with production-like settings to catch these issues early. If you're working in a team, document this fix in your project's troubleshooting guide so others don't hit the same wall.

Verify the Fix

After applying the fix, restart your TypeScript application and verify the error no longer appears in the console or logs. Test both the happy path and edge cases to be thorough. If the error persists, double-check that your changes were saved and the application fully restarted.

Prevention

Tip: Use [Bugsly](https://bugsly.dev) to automatically detect and alert you to TypeScript errors like this in production before your users notice them.