How We Refactored 500k LOC from Vue 3.3 to 3.4 with Vite 6 and TypeScript 5.6 Large-scale codebase migrations are often fraught with risk: downtime, regressions, and developer productivity loss. When our team decided to upgrade our 500,000-line-of-code (LOC) Vue application from Vue 3.3 to 3.4, pair the upgrade with Vite 6 and TypeScript 5.6, we knew we needed a meticulous, incremental approach to avoid disruption. This article walks through our planning, execution, and lessons learned from one of the largest frontend migrations our team has ever undertaken. Why We Upgraded Our application, a enterprise resource planning (ERP) tool used by 10k+ daily active users, was running on Vue 3.3, Vite 5, and TypeScript 5.5. We had three core drivers for the upgrade: first, Vue 3.4 stabilized key features we’d been testing in experimental mode, including defineModel and improved reactive performance. Second, Vite 6 promised 30% faster build times and better environment isolation for our micro frontend modules.…