What do you do when React Router v5 is blocking your React 18 upgrade, your frontend spans 25 repos, and you have 5 different micro frontend strategies running in the same app?
In this episode of Señors at Scale, Dan Neciu sits down with Nicolas Beaussart-Hatchuel, Staff Engineer at PayFit and maintainer of TanStack Router. Nicolas shares the full story of migrating a 1.5 million-line codebase from React Router v5 to TanStack Router using the strangler pattern, without big-bang migrations and without stopping 18 engineers from shipping 15-20 PRs a day.
We also dive into the origin story of TanStack Router, why PayFit killed micro frontends entirely and moved back to a single monorepo, how building the whole app at once saved 25MB of JavaScript, and why his MCP experiments performed worse than simply letting AI agents read the code. Plus: what it really takes to go from senior to staff engineer.
Key Topics:
- How Nicolas got into coding and his first iframe-based micro frontend migration
- The origin story of TanStack Router and URL-as-state
- Migrating 1.5M lines from React Router v5 to TanStack Router
- The strangler pattern applied to frontend migrations
- Faking React Router providers to sync two routers on one URL
- Consolidating 25 repos into one monorepo
- Secret dependencies, Yarn v1 pain, and standardizing on Vite
- Why dropping per-library builds saved 25MB of JavaScript
- TypeScript Go in editors and its RAM cost
- MCP servers vs agents reading code directly
- Internal DevRel: winning engineers over with social proof
- Going from senior to staff: system design and finding problems worth solving
- What's next: TanStack Start v1 and parallel routes
Connect with Nicolas:
💼 LinkedIn: https://www.linkedin.com/in/beaussan/
🐦 X: https://x.com/beaussan
🐙 GitHub: https://github.com/beaussan
🌐 Website: https://beaussan.io
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💼 Dan's LinkedIn: https://www.linkedin.com/in/neciudan
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ADDITIONAL RESOURCES:
- TanStack Router: https://tanstack.com/router
- Engineering Management for the Rest of Us by Sarah Drasner
- Scaling Fast by Swizec Teller
- Swizec's newsletter: https://swizec.com
#TanStackRouter #React #Monorepo #MicroFrontends #FrontendArchitecture #TypeScript #StaffEngineer #SenorsAtScale
💬 Have you ever had to migrate a router in a live codebase? What pattern did you use? Drop it in the comments.
