TypeScript
Types that catch bugs before your users do.
For developers who know JavaScript: the type system from annotations to generics, narrowing, utility types, real-project configuration and typing React - with free resources on every topic.
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- 1
Getting Started
TS running, and the philosophy understood.
1 week0/3Static checking at build time, erasure at runtime - TS is JavaScript with a spell-checker for logic.
Free resources
When to annotate and when inference does it better - typing variables, params and returns.
tsconfig, build vs watch, and how editors surface errors as you type.
Free resources
- 2
Everyday Types
Type real application data confidently.
1–2 weeks0/4Shaping data with interface and type, optional/readonly members, extending and intersections.
Free resources
Modelling real states ('loading' | 'error' | 'success') so invalid states can't compile.
Typed collections, fixed-shape tuples, and why const objects often beat enums.
Call signatures, optional params, overloads and typing callbacks.
Free resources
- 3
Narrowing & Guards
Let the compiler prove your code safe.
1–2 weeks0/4typeof, in, instanceof and truthiness checks - how TS follows your ifs and narrows types with you.
Free resources
A shared literal tag turns unions into exhaustive switch statements the compiler audits for you.
Custom guards (x is Fish), as-casts and never - and why every assertion is a small IOU.
unknown forces proof before use; any turns the checker off. Learning to prefer the former is the TS growth moment.
- 4
Generics & Advanced Types
Reusable code that stays type-safe.
2 weeks0/4Type parameters and constraints (extends) - writing once for many types without losing safety.
Free resources
Partial, Pick, Omit, Record, ReturnType, Awaited - the standard library of type transformations.
Free resources
Deriving types from values and objects - one source of truth instead of parallel definitions.
Enough to read library types and error messages without fear - writing them comes later.
- 5
TS in Real Projects
Use TS the way teams do.
2 weeks0/4strictNullChecks and friends - the flags that make TS worth using, on from day one.
Props, state, events, children and generic components - typed UI end to end.
Free resources
Reading .d.ts, @types packages and typing untyped dependencies.
Runtime validation (e.g. zod) where data enters - types checked at compile time, data checked at runtime.
Free resources
Build: Migrate a JS project to strict TS
Convert a small JS app to strict-mode TypeScript - the fastest way to internalise the system.
- 6
Prove It
Verified proof of TS fluency.
1 week0/1Take the OneRoadmap TypeScript certification - verified, shareable proof.
Free resources