Prove your TypeScript skills
Plenty of code is technically TypeScript and still full of any. Lemma shows whether you design types that model your domain, through live sessions, adaptive assessments and repositories you connect.
Preparing for an interview? TypeScript interview questions, junior to senior
What TypeScript competence looks like
A strong TypeScript developer uses the type system to make invalid states impossible. They reach for discriminated unions instead of optional flags, narrow types with guards rather than casts, and treat an escape hatch like any or a non-null assertion as a decision that needs a reason.
They also read and write generics comfortably, type third-party data at the boundary with runtime validation, and keep compiler settings strict. When a type error appears in a large codebase, they can follow it back to the source and fix the model instead of patching the symptom.
Type design review in a live session
60 min · Learning · with Ava T.
Ava T. rated the session
Practitioner · after the call
Clear reasoning on type narrowing. Talked through trade-offs first.
Type narrowing
Type guards, discriminated unions and exhaustive checks that let the compiler prove each branch is handled.
Generics
Writing reusable functions and components with constraints, defaults and inference that stays readable.
Utility and mapped types
Partial, Pick, Record and custom mapped or conditional types used to derive types instead of duplicating them.
Typing at the boundaries
Validating API responses and user input at runtime so the static types can be trusted.
Strict compiler settings
Strict null checks, no implicit any, and migrating a loose codebase toward strictness safely.
Declaration files
Typing untyped libraries, module augmentation and publishing accurate types for your own packages.
What counts as evidence of TypeScript skills?
Listing TypeScript on a profile proves nothing on its own. What counts is a component you shipped, a session where someone watched you debug one, or a test you passed. These are the records Lemma can hold for your TypeScript skill, and where each one comes from. See the evidence methodology for how each source is weighed.
TypeScript
Clara W. · SCI recomputed 9 Oct
Evidence · 4 entries
- Rated 5.0
Type design review in a live session
Live session · 9 Oct
- Level 7.2
Adaptive TypeScript assessment
Adaptive assessment · 2 Oct
- Verified
A strictly typed repository
GitHub connector · 24 Sep
- Taught · 1.5x
Teaching TypeScript to a peer
Live session · 11 Sep
Type design review in a live session
Model a small domain with a practitioner, such as order states or API responses. They see whether you choose unions, generics and guards well, and rate the session.
Adaptive TypeScript assessment
Scenarios test narrowing, generic constraints and inference. Some show code with a type error or an unsafe cast, and you pick the change that models it correctly.
A strictly typed repository
Connect a GitHub repository or commit that shows your types, for example a migration to strict mode. Lemma checks it exists and that you can access it.
Teaching TypeScript to a peer
Explaining generics or narrowing to someone learning them shows depth. Teaching sessions count for more than learning ones in your record.
How is a TypeScript skills test run on Lemma?
The TypeScript test is adaptive: 15 to 25 questions, each picked from how you answered the last, built around real interface bugs rather than trivia. Its result joins your live sessions and linked repositories or deployments in your TypeScript SCI, which also weighs how recent the evidence is.
Which type best models a request that is loading, failed or done?
- AA discriminated union on a status field
- B{ loading?: boolean; error?: Error; data?: T }
- Cany, narrowed with casts where needed
- DPartial<Response<T>>
Model types with a practitioner
In a live session you design types for a real problem and defend your choices. Expect to be asked why you used a union, where a cast is hiding a bug, and how the types guide callers.
Take the adaptive assessment
Questions start from your level and adjust after each answer. Realistic scenarios cover narrowing, generics and utility types; harder ones count for more, and each has a time limit.
Back it with real code
Connect a GitHub repository written in strict TypeScript. Your sessions, assessment result and connected code sit together under one TypeScript skill on your Passport.
TypeScript skills: common questions
How do employers check TypeScript skills beyond the CV?
What advanced TypeScript features should I learn for a mid-level role?
Does TypeScript evidence on Lemma count toward JavaScript too?
How do I prove TypeScript experience from a codebase migration?
Skills related to TypeScript
Browse the skills directoryJavaScript
Evidence that you understand how JavaScript runs, not just how to write its syntax.
Evidence for JavaScriptReact
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Evidence for ReactNode.js
Evidence of how you build and debug Node.js services, from the event loop to production errors.
Evidence for Node.jsAngular
Evidence for structuring large Angular apps with services, RxJS and change detection.
Evidence for Angular
Start your TypeScript evidence record.
Lemma is in early access. Request an invite and we will email you when your place is ready.