Migrating from Vue 2 to Vue 3 Without a Rewrite

Stage the work, do not heroize it

• Inventory first: list dependencies with Vue 3 support gaps; Vuetify, old router plugins, and abandoned component libraries decide your critical path.
• Modernize tooling: move to Vite and current test runners while still on Vue 2.7, which backports <script setup> and the Composition API so new code is written Vue 3 style before the switch.
• Flip with the migration build: @vue/compat runs Vue 3 with Vue 2 behavior, warning on every deprecated pattern; burn the warnings down module by module.
• Finish: drop compat mode, swap Vuex for Pinia where convenient, and let new features pay the dividend.

The breakage that actually bites

Most templates survive untouched. What bites: filters (gone, become computeds or methods), $on/event-bus patterns (gone, become composables or a tiny emitter), v-model on components (renamed prop and event), and functional components (plain functions now). Reactivity's Proxy rewrite removes the old array-index and property-addition caveats, which fixes more bugs than it creates, but any code that relied on those caveats needs a look.

Keep shipping while migrating

Budget the migration as a stream of small pull requests alongside features, not a freeze. Component tests are your safety net, and the modules with none get them first, since the migration will stress exactly the code nobody understands anymore. Teams that stage it this way consistently report the same surprise: the dread was worse than the work.