Browser Polyfills for Next.js

Core Philosophy

• Fix what's broken, not what's theoretical. Check caniuse before adding polyfills.
• Load polyfills conditionally. Modern browsers should not pay for Safari's gaps.
• Safari on iOS is the primary target. All iOS browsers use WebKit, so a Safari bug affects Chrome on iPhone too.
• Prefer CSS workarounds over JavaScript polyfills when possible — zero runtime cost.
• Never use polyfill.io — it was compromised in 2024. Self-host or use Cloudflare's mirror.

Quick-Start: Diagnosing What Broke

"My app works in Chrome but breaks in Safari"