So You Decided to Do a Technical Migration
summary
Monzo migrates its web codebase from Flow to TypeScript using a set of homegrown tools: a migration script that bootstraps packages and generates Flow shims, a dependency finder that unlocks packages, and a progress dashboard that shows Flow vs TypeScript lines crossing. The effort runs just over two years, uses incremental app-by-app work and ticketed milestones, reaches ~97–99% before final removal of Flow, yields faster compile times, exposes missing props, and ultimately succeeds.
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chapters (26)
- 0:00Introduction
- 0:52About Sophie
- 3:03About the migration
- 4:40Where to start
- 5:26Before you commit
- 6:26Documentation
- 7:44Who should do it
- 10:52Tooling
- 12:02Migration script
- 13:30Measuring progress
- 14:14Milestones
- 15:01Another Bend in the Road
- 17:36Getting Buy In
- 19:46The Greatest Threat
- 21:46Dealing with Risk
- 25:43Between Phases
- 27:23Celebrate
- 28:05Next time
- 29:38Maintenance
- 30:56New Technology
- 32:05HD DVD
- 33:09deprecated technologies
- 35:05is it worth it
- 35:17is it really worth it
- 35:34choose boring technology
- 36:27conclusion
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