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004-typescript-migration.md

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ADR 004: Migrate to TypeScript

Status: Accepted
Date: January 2026
Deciders: Engineering Team

Context

The codebase is currently JavaScript with JSDoc hints. As the project grows (566 files), type safety becomes increasingly important to prevent bugs and improve developer experience.

Decision

We will migrate the entire codebase to TypeScript over Q2-Q3 2026.

Rationale

Pros:

  • Type safety catches bugs at compile time
  • Better IDE support and autocomplete
  • Improved refactoring confidence
  • Self-documenting code
  • Easier onboarding for new developers
  • Industry standard for large React projects
  • Base44 backend already uses TypeScript

Cons:

  • Significant migration effort (566 files)
  • Learning curve for team members
  • Longer build times
  • More verbose code

Migration Plan

Phase 1 (Q2 2026):

  • Add TypeScript to build pipeline
  • Convert utilities and hooks (small files first)
  • Target: 25% conversion

Phase 2 (Q3 2026):

  • Convert components
  • Convert pages
  • Target: 75% conversion

Phase 3 (Q4 2026):

  • Complete remaining files
  • Remove JSDoc annotations
  • Target: 100% TypeScript

Consequences

Positive:

  • ✅ Fewer runtime errors
  • ✅ Better developer experience
  • ✅ Easier refactoring
  • ✅ Better documentation through types

Negative:

  • ⚠️ Migration takes 2-3 months
  • ⚠️ Temporary mixed codebase
  • ⚠️ Slightly slower builds