Lesson 15 — Generic functions

Generic helpers for arrays

When a function takes an array, T[] means "an array of some type T", and returning T means "one item of that same type". If the array may be empty, be honest and return T | undefined — TypeScript will then remind callers to handle the missing case.

function last<T>(items: T[]): T | undefined {
  return items[items.length - 1];
}
last([1, 2, 3]); // number | undefined

Why it matters: small generic helpers like this get reused all over a codebase with full type safety.