Lab · Intermediate · 30 min
Lab: Find the bug the types missed
Given a module with a runtime bug that loose types allowed, tighten the types until the compiler finds it.
- A pricing function occasionally returns NaN in production. The types say everything is a number.
Tasks 3
Project · Intermediate · 6h
Project: Type a legacy module properly
Take an untyped or loosely typed module and give it precise types: unions, boundaries, strict mode, no any.
- Choose a real module with any, string-typed enums or unchecked JSON. Model its data with discriminated unions and literal types, add schema parsing at its boundaries, enable strict for it, and remove every any and cast. Keep behaviour identical, proven by tests or snapshots.
- Milestone 1: Safety net
- Milestone 2: Model
Learning path · Intermediate · 6h
TypeScript that catches real bugs
Types as a tool for correctness: modelling data, narrowing, generics and strictness that pays for itself.
- Write TypeScript that models data precisely, narrows safely and stays strict without fighting the compiler.
- Skills: Modelling data with unions and literal types, Narrowing with guards, Generics that stay readable, Strict configuration, Typing at boundaries
Time 6h

Instant delivery after paymentLicence stated on every productRe-download anytime from My LibrarySecure checkout — Polar or FungiesNew products every week

Products GamingNew Subscriptions Deals Membership Licensing

Search

Lab: Find the bug the types missed

Project: Type a legacy module properly

TypeScript that catches real bugs