Annotate parameters and return types: function add(a: number, b: number): number. Arrow functions support the same.
void means no useful return; undefined is a value type.
Optional and default parameters
function connect(host: string, port = 443) keeps call sites short. Explicit return types on exported functions document contracts even when inference would work.
Self-check
- Add a function with an optional parameter and a union return type.
Practice: Apply typed-functions in the playground, then explain typed functions in one sentence without looking at notes.