TypeScript reached 43.6% usage in the 2025 Stack Overflow Developer Survey—often bundled with JavaScript on professional teams (Stack Overflow 2025 Technology). Hiring for “TS experience” on a resume is easy; hiring for type discipline is harder.
These five questions surface judgment on strict typing, narrowing, generics, shared API contracts, and pragmatic migration—not whether they can recite interface vs type.
1. “What breaks when you turn on strictNullChecks in an existing codebase?”
Strong candidates describe real migration work: optional chaining, discriminated unions, fixing implicit any, and staged rollouts. Weak answers treat strict mode as a linter preference.
2. “How do you narrow a union type at runtime without unsafe casts?”
Type guards, in checks, and exhaustiveness in switch reveal whether they use the type system for safety or paper over gaps with as. This mirrors how professional TS interviews test narrowing beyond basics.
3. “How would you type a generic API wrapper that handles success and error responses?”
Generics with constraints show up in modern full-stack hiring screens. Listen for discriminated unions, reusable helpers, and avoiding any in the public surface.
4. “How do you keep frontend and backend types from drifting apart?”
Good answers mention shared packages, OpenAPI/codegen, contract tests, or monorepo boundaries—whatever matches your stack. The point is process, not one magic tool.
5. “Tell me about a time TypeScript caught a bug before production—or failed to.”
You learn humility and calibration. Strong candidates admit where types were too loose or @ts-ignore crept in and what they changed afterward.
Turn answers into comparable evidence
Log one strict-mode migration story, one narrowing pattern they prefer, one API typing approach, and one honest limit of their TS setup. Compare facts, not buzzwords.
One scorecard for every finalist
Use the same five questions for each candidate for this opening. Consistent questions support consistent evaluation, which aligns with EEOC guidance for employers to apply the same standards to applicants for the same position (EEOC).
Use Canvider JobCraft to spell out TypeScript level and framework context in the JD, InterviewGen for gap-based follow-ups, and DecisionHelper to compare finalists on the criteria you published.
Next step: Explore InterviewGen and DecisionHelper, then get started free.