TypeScript Development as a Subscription

Why TypeScript is non-negotiable

Every project we build uses TypeScript. Not because it is trendy, but because it pays for itself within the first month. The data is clear:

• Airbnb reported that 38% of bugs in their codebase could have been prevented by TypeScript
• Bloomberg estimated a 30% reduction in production bugs after migrating to TypeScript
• Projects using TypeScript have 15% fewer bugs in pull requests (GitHub study)

TypeScript is not about writing more code. It is about writing code that communicates its intent, catches mistakes before they reach users, and makes refactoring safe instead of terrifying.

The real cost of JavaScript

In a pure JavaScript codebase:

• Every function call is a guess. What shape does that object have? Is that parameter optional? Can it be null? You only find out at runtime.
• Refactoring is dangerous. Rename a property and hope you found every reference. Miss one, and it fails silently in production.
• Onboarding is slow. New developers spend days reading code to understand data shapes that TypeScript would document automatically.
• Tests compensate for missing types. You write tests to verify things the compiler should catch for free.

Read more about reducing bugs and rework: Reducing Technical Debt

What TypeScript gives you

Compile-time safety

TypeScript catches entire categories of bugs before your code ever runs:

// JavaScript: fails silently at runtime
function getUser(id) {
  return fetch(`/api/users/${id}`).then(r => r.json())
}
// What does the response look like? Nobody knows.

// TypeScript: everything is explicit
async function getUser(id: string): Promise<User> {
  const response = await fetch(`/api/users/${id}`)
  return response.json() as User
}
// Now every consumer knows exactly what they get.

IDE superpowers

With TypeScript, your editor becomes intelligent. Auto-complete, inline documentation, go-to-definition, find-all-references, and rename-across-project work reliably because the compiler understands your code.

Living documentation

TypeScript interfaces and types serve as documentation that never goes stale. When you change a type, every file that uses it shows a compile error immediately. No more outdated README files or API docs that drift from reality.

Safe refactoring

Need to change the shape of a database model? Change the Prisma schema, regenerate the types, and the compiler tells you every file that needs updating. What used to be a week of careful manual changes becomes an afternoon of guided fixes.

JavaScript to TypeScript migration

Migrating an existing JavaScript codebase to TypeScript is one of our most requested services. We have migrated codebases ranging from 5,000 to 500,000 lines of code. Here is our proven approach.

The incremental strategy

We never recommend a big-bang migration. Instead:

Phase 1: Setup (Week 1)

• Add tsconfig.json with strict: false and allowJs: true
• Configure ESLint with @typescript-eslint
• Set up the CI pipeline to check TypeScript errors
• Rename entry files from .js to .ts

Phase 2: Low-risk migration (Weeks 2-4)

• Rename utility files and shared modules to .ts
• Add types to function signatures (parameters and return types)
• Replace any with proper types where the shape is obvious
• Add @ts-check comments to remaining .js files

Phase 3: Core business logic (Weeks 4-8)

• Migrate API layer, database models, and middleware
• Define shared interfaces for API contracts
• Replace any in complex areas with proper generics
• Enable strict: true module by module

Phase 4: Strict mode everywhere (Weeks 8-12)

• Enable strict: true globally
• Remove all any types (or replace with explicit unknown)
• Add noUncheckedIndexedAccess for maximum safety
• Remove the allowJs flag

Migration cost vs benefit

Metric	Before migration	After migration
Production bugs (monthly)	12-15	3-5
Average PR review time	45 min	25 min
Onboarding time (new dev)	3 weeks	1 week
Refactoring confidence	Low	High
IDE auto-complete accuracy	~40%	~98%

The migration typically pays for itself within 3 months through reduced bugs and faster development velocity.

Monorepo setups with TypeScript

For projects with multiple applications sharing code (frontend + backend, web + mobile admin, multiple microservices), we set up TypeScript monorepos.

Turborepo configuration

Turborepo is our tool of choice for TypeScript monorepos. It provides:

• Incremental builds: Only rebuild what changed
• Remote caching: Share build artifacts between developers and CI
• Task orchestration: Build dependencies in the correct order
• Workspace management: Shared dependencies, consistent versions

Typical monorepo structure

apps/
  web/           # Next.js frontend
  api/           # NestJS backend
  admin/         # React admin panel
packages/
  shared-types/  # TypeScript interfaces shared across apps
  ui/            # Shared component library
  config/        # ESLint, TypeScript, Prettier configs
  utils/         # Shared utility functions

The shared-types package is the critical piece. API request/response types, database models, enums, and constants are defined once and imported everywhere. Change a type in one place, and every application that uses it gets a compile error if the contract breaks.

Shared types between frontend and backend

This is where TypeScript truly shines. With a Node.js backend and a React frontend, you can share types end-to-end:

1. Prisma generates TypeScript types from your database schema
2. Shared types package defines API contracts (request/response shapes)
3. Frontend imports those types and gets compile-time validation of every API call
4. tRPC (optional) eliminates the serialization boundary entirely

No more mismatches between what the API sends and what the frontend expects. No more runtime surprises.

Zod: Runtime validation meets TypeScript

TypeScript types disappear at runtime. They cannot validate user input, API responses, or environment variables. That is where Zod comes in.

Zod lets you define a schema once and derive both the runtime validation and the TypeScript type from it:

import { z } from 'zod'

const UserSchema = z.object({
  id: z.string().uuid(),
  email: z.string().email(),
  name: z.string().min(1).max(100),
  role: z.enum(['admin', 'user', 'viewer']),
})

// TypeScript type derived from the schema
type User = z.infer<typeof UserSchema>

// Runtime validation
const result = UserSchema.safeParse(apiResponse)
if (!result.success) {
  // Handle validation error with detailed error messages
}

We use Zod for:

• API input validation in NestJS (replacing class-validator)
• Environment variable validation (fail at startup, not at runtime)
• Form validation in React (with react-hook-form)
• External API response validation (never trust third-party data)

tRPC: End-to-end type safety without GraphQL

For projects where frontend and backend live in the same monorepo, tRPC provides end-to-end type safety without code generation or a schema language.

tRPC vs GraphQL vs REST

Feature	REST	GraphQL	tRPC
Type safety	Manual (OpenAPI)	Code generation	Automatic
Client code generation	Needed	Needed	Not needed
Schema language	OpenAPI/YAML	SDL	TypeScript
Learning curve	Low	Medium	Low
External consumers	Ideal	Good	Not suitable
Same-monorepo frontend	Fine	Fine	Ideal
Performance overhead	None	Query parsing	None

Our recommendation: Use tRPC when frontend and backend are in the same monorepo and you do not need external API consumers. Use GraphQL when you need flexible queries for multiple clients. Use REST when you need maximum interoperability.

TypeScript configuration best practices

We configure every project with maximum safety:

{
  "compilerOptions": {
    "strict": true,
    "noUncheckedIndexedAccess": true,
    "noImplicitReturns": true,
    "noFallthroughCasesInSwitch": true,
    "exactOptionalPropertyTypes": true,
    "forceConsistentCasingInFileNames": true,
    "isolatedModules": true,
    "verbatimModuleSyntax": true
  }
}

Why strict mode matters:

• strictNullChecks: Forces you to handle null and undefined explicitly
• noUncheckedIndexedAccess: Array access returns T | undefined, not T
• exactOptionalPropertyTypes: Distinguishes between undefined and "not present"
• verbatimModuleSyntax: Ensures import/export syntax matches the module system

These settings catch bugs that even experienced developers miss. The compiler is your most reliable code reviewer.

Common questions about TypeScript development

Is TypeScript worth it for a small project?

Yes. Even for a 500-line script, TypeScript catches bugs, provides auto-complete, and makes the code self-documenting. The overhead is minimal: one tsconfig.json file and a build step.

Will TypeScript slow down my team?

Short-term, there is a learning curve of 1-2 weeks for developers new to TypeScript. Long-term, TypeScript accelerates development because refactoring is safe, documentation is automatic, and an entire category of bugs disappears. Studies consistently show a net positive within the first month.

Can you migrate my JavaScript project to TypeScript?

Yes. We have migrated projects from small utilities to large SaaS platforms. Our incremental approach means your application keeps running throughout the migration. No feature freeze required.

Should I use any when I am stuck?

Never as a permanent solution. any disables type checking and defeats the purpose of TypeScript. If you genuinely cannot type something, use unknown and narrow it with runtime checks. We use ESLint rules to flag and prevent any in production code.

What does TypeScript development cost?

TypeScript is included in every subscription plan. It is not an add-on; it is how we build everything. Plans start at €2,495/month. Compare options: Freelancer vs Agency vs Subscription.

How do you handle third-party libraries without types?

Most popular libraries have TypeScript types (either built-in or via @types/*). For the rare library without types, we write a declaration file (.d.ts) with the minimum types needed. We never use any as a workaround.

Related services

• React Development: TypeScript-first React applications
• Next.js Development: Full-stack TypeScript with Next.js
• Node.js Backend: TypeScript backend with NestJS and Prisma
• API & Integration Development: Type-safe APIs with OpenAPI and tRPC
• Mobile Development: Swift and Kotlin share the type-safety philosophy
• Design System: Typed component APIs with Storybook