TypeScript Modernization Services
We convert JavaScript codebases to TypeScript file by file, while your team keeps shipping. Fewer runtime surprises, safer refactoring, and an editor that actually understands your code.
- Type Safety
- Incremental Migration
- Ship While Migrating
Why Migrate to TypeScript?
Catch Bugs Before Production
The compiler checks types, null references and API mismatches while the code is being written, not after a user hits them. A whole class of production errors simply stops compiling.
- Errors surface at compile time, not in production
- strictNullChecks stops undefined-access crashes
- Function signatures enforce API contracts
- Rename and restructure with the compiler watching
Improve Developer Experience
With real types, the editor knows what your code means. Autocomplete that is actually correct, rename-symbol that works across the whole codebase, and types that serve as documentation which cannot go stale.
- Autocomplete driven by actual types, not guesses
- Automated refactoring the compiler verifies
- Types document intent where comments drift
- New developers read the code instead of reverse-engineering it
Common JavaScript Pain Points We Solve
Runtime Errors
"Cannot read property 'x' of undefined" and its relatives, which have a habit of appearing only in production.
TypeScript Solution: strictNullChecks turns them into compile errors
API Integration Bugs
The backend renames a field, the frontend finds out in production. Nothing in the toolchain connects the two.
TypeScript Solution: Types generated from your OpenAPI or GraphQL schema
Refactoring Fear
Nobody dares restructure the code because nobody can say what breaks. So the code stays the way it is.
TypeScript Solution: The compiler lists every call site a change affects
Our TypeScript Migration Services
Incremental Migration
- Codebase analysis and a file-level migration plan
- Conversion order that follows the dependency graph
- tsconfig.json set up for gradual adoption
- Compiler strictness raised step by step
- JS and TS coexist, so releases continue as usual
- Every step is a normal commit you can revert
Type Definition Creation
- Custom .d.ts files for your own modules
- Types for third-party libraries that ship none
- API types generated from OpenAPI specs
- Database types via Prisma or similar
- Shared utility types for recurring patterns
- Written notes on the type decisions we made
Codebase Modernization
- ES2022+ syntax where it makes the code clearer
- Callback and promise chains rewritten as async/await
- CommonJS to ESM module migration
- Class components moved to React Hooks
- Pure functions where mutation causes bugs
- One formatter, one lint config, no debates
Testing & Quality
- Unit tests moved to Vitest or kept on Jest
- Test helpers and fixtures with proper types
- Integration tests updated alongside the code
- E2E tests in Playwright where they earn their keep
- Type coverage measured and tracked per package
- CI updated to type-check every pull request
Strict Mode Enablement
- The road from loose config to `strict: true`
- Null and undefined handled explicitly everywhere
- Implicit any removed, file by file
- Dead code and unused variables cleaned out
- typescript-eslint rules that stop regressions
- Conventions your team agrees to and CI enforces
Team Training
- TypeScript fundamentals workshop for the team
- Advanced types: narrowing, unions, inference
- Patterns that work and the ones to avoid
- Generics and utility types in real code
- How to keep migrating after we leave
- Ongoing consultation when questions come up
Our 4-Phase Migration Process
Assessment & Planning (Week 1-2)
2 weeksWe read the code before we promise anything. Static analysis, a dependency audit, and interviews with the people who maintain it. The result is a file-level plan with the risks named, not a slide deck.
Deliverables:
- Migration plan, down to file level
- Risk list with mitigations
- Timeline and staffing proposal
Activities:
- Static code analysis
- Dependency graph mapping
- Team interviews
Success Metrics:
- Whole codebase reviewed
- Plan approved by your team
- Everyone knows the order of work
Foundation Setup (Week 3-4)
2 weeksTypeScript compiler and build pipeline configured so JS and TS compile side by side. We convert a first slice of files to prove the setup works in your CI, not just on our machines.
Deliverables:
- tsconfig.json tuned for gradual migration
- Build and CI pipeline type-checking TS
- First 10-20% of files converted
Activities:
- Compiler and build setup
- Type definitions installed
- CI/CD updates
Success Metrics:
- CI green with mixed JS/TS
- No change visible in production
- Your team writing TS daily
Incremental Migration (Week 5-10)
6 weeksFiles convert in dependency order, leaf modules first, so types flow outward without blocking anyone. Feature work continues in the same repo the whole time; conversion lands as ordinary reviewed pull requests.
Deliverables:
- 80-90% of files converted
- Type coverage tracked per package
- Visible progress, week by week
Activities:
- Weekly conversion batches
- Code reviews with your team
- Knowledge transfer sessions
Success Metrics:
- Type coverage target reached
- Test suite green throughout
- No production incidents caused by the migration
Strict Mode & Optimization (Week 11-12)
2 weeksWe turn on `strict: true`, remove the remaining any types, add type guards where the data warrants them, tune compile times, and write down the conventions so the codebase stays this way.
Deliverables:
- `strict: true` on across the codebase
- Conventions documented in the repo
- Shared type library for common models
Activities:
- Strict mode enablement
- Build time tuning
- Final team workshop
Success Metrics:
- No `any` left in the code
- Type coverage at agreed target
- Team runs the codebase without us
Ready to Modernize Your JavaScript Codebase?
Book a free migration assessment. We run the compiler and our analysis tooling over your codebase and come back with a concrete plan: conversion order, risks, timeline and cost estimate.