TypeScript Generics: A Practical Guide for Backend Developers

#typescript #webdev #programming #backend

TypeScript Generics: A Practical Guide for Backend Developers

Generics let you write reusable, type-safe code without duplicating functions or using any.

The Basics

function getFirst<T>(items: T[]): T | undefined { return items[0]; }
const num = getFirst([1, 2, 3]); // type: number

Generic API Response

interface ApiResponse<T> { data: T; meta: { page: number; total: number }; }

async function fetchPaginated<T>(url: string): Promise<ApiResponse<T>> {
  return (await fetch(url)).json();
}

Generic Repository

class Repository<T extends HasId> {
  constructor(private collection: string) {}
  async findById(id: string): Promise<T | null> {
    return db.collection(this.collection).findOne({ id });
  }
  async create(data: Omit<T, "id">): Promise<T> {
    const doc = { ...data, id: randomUUID() } as T;
    await db.collection(this.collection).insertOne(doc);
    return doc;
  }
}