Modernizing a full Angular app in 3 days with AI assistance

Problem

The team’s main Angular application was stuck on v12 — nine major versions behind — while a prior manual modernization attempt had already burned two weeks and was still incomplete. Every version jump between v12 and v22 changes real internals: the dependency-injection story, the compiler, module boundaries, and eventually the rendering model itself with Zoneless change detection. A half-migrated app is worse than an old one: mixed patterns, doubled bundle weight from parallel APIs, and a build pipeline nobody fully trusted.

Solution

Rather than attempting another manual big-bang migration, I paired AI-assisted tooling with a step-by-step upgrade path across all nine major versions, verifying framework behavior at each stop instead of skipping straight to the target. Standalone components replaced NgModules where it mattered, Signals replaced manual change-detection triggers, and the app was moved onto Zoneless change detection once the rest of the surface area was stable. AI acceleration handled the mechanical, repetitive parts of the migration (codemods, import rewrites, dependency bumps); the judgment calls — what’s actually safe to remove, what still needs a compatibility shim, what changes user-visible behavior — stayed manual.

Impact

• The full v12 → v22 migration completed in 3 days, versus two incomplete weeks on the earlier manual attempt.
• Bundle size dropped from ~50MB to 8MB.
• Build time came down to 15 seconds.
• The approach — AI for mechanical migration work, human judgment for anything with real risk — became the team’s standard playbook for large-scale upgrades, later reused for the company-wide vulnerability-mitigation process.