Generics

function loggingIdentity<T>(table: T[]): string {
  return `Total elements in the table: ${table.length}`;
}

Constraints

type Product = { id: number; name: string; price: number };

function getTotal<T extends Product>(products: T[]): string {
  const totalPrice = products.reduce((sum, p) => sum + p.price, 0);
  return `There are ${products.length} products. And the total price is ${totalPrice}.`;
}

Parameter Defaults

type ApiResponse<T = string> = { data: T; success: boolean; };

const response1: ApiResponse = { data: "OK", success: true };
const response2: ApiResponse<number> = { data: 200, success: true };

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TypeScript: Documentation - Generics