TypeScript

The type system as a reasoning tool, not a chore — generics, narrowing, inference, and where it echoes ideas JavaScript already had.

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Structural TypingIntermediateTypeScript decides if two types are compatible by comparing their shape, not their name — the same instinct as JavaScript's own duck typing, checked one phase earlier.13 min · 0/3 questions correct
Interfaces vs Type AliasesIntermediateBoth describe a shape, and for plain object types they're nearly interchangeable — but each can do something the other genuinely cannot.11 min · 0/3 questions correct
Narrowing & Discriminated UnionsAdvancedA union type can't be used as any specific member until you prove which one it is — and checking one shared property can narrow an entire object at once.15 min · 0/3 questions correct
GenericsIntermediateA generic is a placeholder for a type, filled in at the call site — the same instinct as a function parameter, one level up.14 min · 0/3 questions correct
any vs unknownIntermediateBoth can hold any value — but any switches off type checking entirely, while unknown forces you to prove what something is before you can use it.11 min · 0/3 questions correct
Type Inference & as constIntermediateTypeScript infers types from values without annotations — but it 'widens' literals by default, and as const is how you opt out.12 min · 0/3 questions correct
Utility TypesIntermediatePartial, Pick, Omit, and Record aren't special compiler magic — they're ordinary generics built from mapped types, the same tools available to you.13 min · 0/3 questions correct
Custom Type GuardsIntermediateA type guard is a promise you make to the compiler — a function whose return type tells TypeScript to actually trust and narrow, not just a boolean check.12 min · 0/3 questions correct
TypeScript with ReactIntermediateTyping a component is just typing a function — props are parameters, JSX is the return value. Everything from the last 8 lessons applies directly.14 min · 0/3 questions correct
EnumsIntermediateA named set of related constants — genuinely useful, but the one TypeScript feature that generates real runtime JavaScript, which is exactly why the community increasingly reaches for a plainer alternative instead.11 min · 0/2 questions correct
TuplesIntermediateAn array type that knows its exact length and the specific type of each position — turning `useState`'s [value, setter] return from a lucky guess into an actually-checked contract.10 min · 0/2 questions correct
Literal TypesIntermediateA type that describes not just 'a string' but one exact string — the mechanism that turns a specific value into something the compiler can check against, and what narrowing is actually narrowing down to.10 min · 0/2 questions correct