tsyringe

import "reflect-metadata"; // Must be imported ONCE at the very top of your application entry point import { container, injectable, inject, singleton } from "tsyringe"; // 1. Define an interface for abstraction interface IDatabaseService { connect(): void; getData(query: string): string; } // 2. Implement the interface and mark as injectable @injectable() class RealDatabaseService implements IDatabaseService { connect() { console.log("Connected to a real database."); } getData(query: string): string { return `Data for: ${query} from RealDatabase`; } } // 3. Define a service that depends on IDatabaseService @injectable() class DataProcessorService { constructor(@inject("IDatabaseService") private dbService: IDatabaseService) { this.dbService.connect(); } processUserData(userId: string): string { const query = `SELECT * FROM users WHERE id = ${userId}`; return `Processing user data: ${this.dbService.getData(query)}`; } } // 4. Register the interface with its implementation in the container container.register<IDatabaseService>("IDatabaseService", { useClass: RealDatabaseService, }); // 5. Resolve the DataProcessorService const dataProcessor = container.resolve(DataProcessorService); console.log(dataProcessor.processUserData("123")); // 6. Example of a singleton service @singleton() class AppConfig { public readonly API_KEY = process.env.API_KEY ?? 'default-api-key'; constructor() { console.log("AppConfig initialized (should only happen once for singleton)."); } } const config1 = container.resolve(AppConfig); const config2 = container.resolve(AppConfig); console.log(`API Key: ${config1.API_KEY}`); console.log(`Are config instances identical? ${config1 === config2}`); /* NOTE: Ensure your tsconfig.json includes: { "compilerOptions": { "experimentalDecorators": true, "emitDecoratorMetadata": true } } */