React & TypeScript

Shared state without prop drilling

Some interactions need to reach across the component tree — a scroll-triggered camera move that a footer, a nav bar, and three unrelated section components all need to react to. Threading that through props would mean plumbing state through components that don't otherwise care about it. Instead, a small typed module-level store (a plain object with a `subscribe`/`setActiveIndex` pair) acts as the single source of truth; any component that cares imports it directly and subscribes, any component that doesn't never touches it.

TypeScript is what makes that pattern safe rather than fragile — the store's shape is a real interface, so a call site that gets the contract wrong (wrong argument type, a typo'd method name) fails at compile time instead of silently doing nothing in production.

Types as documentation

Function signatures double as the documentation for how a piece of shared logic is meant to be used — an optional second parameter on a navigation function, for instance, makes an 'instant, skip the animation' fallback path discoverable at the call site instead of buried in a comment three files away.