Part 4.2Generics

Why generics

Generics let one implementation preserve the type supplied by its caller. They are safer than any because the relationship between input and output is retained.

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

const name = first(["Ada", "Lin"]);

Constraints

A constraint states the minimum shape a generic value must have. For example, T extends { id: number } permits code to use id while allowing richer objects.