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Generics

Generics create reusable components that work with multiple types.

Official docs

Generics — typescriptlang.org

Generic Functions​

function first<T>(items: T[]): T | undefined {
  return items[0];
}

const n = first([1, 2, 3]);    // number | undefined
const s = first(['a', 'b']);   // string | undefined

Generic Constraints​

function longest<T extends { length: number }>(a: T, b: T): T {
  return a.length >= b.length ? a : b;
}