React → Next.js at 1M MAU: lessons from tiket.com

At tiket.com I led the migration of the Flight product — serving roughly a million monthly active users — from legacy React to Next.js and TypeScript. A few lessons survived contact with production.

Migrate by route, not by rewrite

A big-bang rewrite at this traffic level is a roadmap-killer. We moved route-by-route, keeping legacy and Next.js surfaces running side by side, so feature work never stopped. Things To Do, the entertainment vertical, followed the same playbook and came out ~50% faster on page loads.

WebViews are your real production environment

A large share of traffic came through in-app WebViews on iOS and Android. Anything you don't test inside a WebView — navigation, auth handoffs, payment redirects — will break inside a WebView. Simulator-driven debugging was a first-class part of the workflow, not an afterthought.

TypeScript pays for itself during the migration, not after

Typing the legacy code as we moved it surfaced years of silent contract drift between frontend and backend. Most of the "migration bugs" we caught were pre-existing bugs that types finally made visible.

Performance budgets beat performance sprints

The ~50% load-time improvement didn't come from one heroic optimization; it came from treating bundle size and Core Web Vitals as budgets enforced in review, so regressions never accumulated into a crisis.