Hire TypeScript Developers for Safer, Clearer Code

How to vet a TypeScript developer

Many developers use TypeScript as JavaScript with occasional annotations. Strong TypeScript developers use the type system to make invalid states impossible: discriminated unions for different shapes of data, generics for reusable functions, strict null checks and types generated from API schemas. They also know when types become too clever and simplify them for teammates.

Ask candidates how they would type an API response, a form with conditional fields or a reducer with several action types. Look for comfort with strict compiler settings, runtime validation libraries such as Zod at system boundaries and tools that keep frontend and backend types in sync. Our TypeScript glossary entry summarizes the core concepts.

Migration experience is especially valuable. Converting a JavaScript codebase gradually, choosing where to start, raising strictness over time and avoiding a flood of any types, takes judgment that many developers have never had to exercise. Ask candidates to describe one migration and what they would do differently.

• Uses discriminated unions and generics appropriately.
• Works with strict mode enabled.
• Validates external data at runtime, not only with types.
• Generates types from OpenAPI or GraphQL schemas.
• Has migrated JavaScript code to TypeScript incrementally.

Interview questions we use for TypeScript developers

We ask candidates to type realistic code and explain their choices. Small exercises, such as typing an API client or refactoring loose types into a union, reveal more than definitions. We also ask how they explain type errors to less experienced teammates, since TypeScript adoption depends on the whole team.

Good answers balance safety and readability. Candidates should explain why types alone cannot protect against bad data from an API, how they keep compile times reasonable in large projects and when they would accept a looser type to keep code understandable.

• How would you model an API response that can be loading, successful or failed?
• When would you use unknown instead of any, and how do you narrow it?
• How do you keep frontend and backend types in sync?
• How would you migrate a large JavaScript project to strict TypeScript?
• What are utility types such as Partial and Pick useful for, and when do they hurt readability?
• How do you validate data from external sources at runtime?

Onboarding a TypeScript developer in the first two weeks

In the first week, the developer reviews the compiler configuration, linting rules and how types flow between modules, APIs and the frontend. They fix small type errors or loose types in areas they touch, which builds familiarity quickly and often reveals hidden bugs. A short written assessment of the type setup helps the team plan improvements.

In week two, they deliver a feature with strong typing end to end and, if a migration is planned, convert one module as a pilot. Our TypeScript vs JavaScript comparison explains the benefits for teams still deciding, and our Node.js developers bring the same typed approach to backend services.