Understanding CORS: Same-Origin Policy and Handling Cross-Origin Requests
Every web developer has at some point seen the dreaded red error: “Access to fetch at ‘http://localhost:8081’ from origin ‘http://localhost:5173’ has been blocked by CORS policy…” Let’s unpack why this happens, why the browser enforces it, and how to handle it cleanly in both development and production. 🧩 What Is an Origin? An origin is defined as the combination of: scheme + domain + port Examples: https://example.com → Origin A https://api.example.com → Origin B (different subdomain) http://localhost:5173 → Origin C (different port) If any of these differ, you’re dealing with cross-origin access. ...