AngularJS to Modern Framework Program Playbook

AngularJS to Modern Framework Program

AngularJS (the 1.x line) reached end of life in January 2022. Applications still running on it carry security, hiring, and performance risk. This playbook runs a controlled program to move a legacy AngularJS codebase to a modern component framework such as React, Vue, or modern Angular, while keeping the product releasable at every step.

The core strategy is the strangler-fig pattern: the new framework runs alongside AngularJS inside one shell, and routes or features migrate one slice at a time. There is no big-bang rewrite.

Phase-by-Phase

Discovery and Inventory. Catalogue every module, directive, controller, and service. Measure existing test coverage; low coverage is the single biggest predictor of migration pain. Choose the target framework with a written decision record so the rationale survives staff turnover.

Foundation and Interop. Stand up modern build tooling (Vite or the framework's CLI). Create an interop shell so the legacy app and new app share routing and a single DOM. Build a small shared component library that both worlds can consume.

Incremental Migration. Migrate one domain at a time, behind feature flags. Port business logic out of AngularJS services into framework-agnostic modules first, then wire up new components. Retire legacy directives as their replacements ship.

Hardening and Cutover. Once the last route is migrated, delete the AngularJS runtime, tune bundle size, and validate accessibility against WCAG 2.2.

Team and Roles

An architect owns the interop boundary and decision records. Frontend engineers do the porting in pairs. QA builds regression coverage ahead of each slice. A product owner sequences domains by business value so the program delivers visible wins early.

Risks and Mitigations

• Regression risk: add characterization tests before touching a module; gate each slice with visual regression checks.
• Scope creep: forbid feature work inside migrated slices until the slice is stable.
• Team coordination: keep one shared component library; do not let teams fork UI primitives.

Success Criteria

The AngularJS runtime is fully removed, median page load improves against the pre-migration baseline, and automated test coverage rises rather than falls during the program.

Tooling

Use a modern bundler (Vite), a component test runner (Vitest), feature-flag infrastructure for slice rollout, and a design-token-driven shared library. Track migrated-route percentage as the headline progress metric.