ERR_CONNECTION_TIMED_OUT

Connection Timed Out caused by browser version differences is less common than in earlier web development eras, but still occurs at the boundaries of new API adoption. The challenge is that users run browsers ranging from current to several years old. The MDN Browser Compatibility table is the definitive reference — it shows the exact version where each API became available in Chrome, Firefox, Safari, and Edge. For JavaScript features, caniuse.com provides market share context alongside version support. The most commonly unsupported modern features causing Connection Timed Out: top-level await (requires modern bundlers for broader support), import maps (supported in Chrome 89+, Firefox 108+, Safari 16.4+), CSS Container Queries (2022–2023 support), and Web Crypto API subtle differences across implementations. Use Babel for JavaScript transpilation and PostCSS for CSS to target older browsers without writing compatibility code manually. For checking which features your actual user base needs, connect Google Analytics with browser version data to determine what percentage of your users run older browser versions that require polyfills.